Merge branch 'master' into master

45 files changed, 3095 insertions, 3297 deletions

diff --git a/db/autocompact_test.cc b/db/autocompact_test.cc
index d20a236..e6c97a0 100644
--- a/db/autocompact_test.cc
+++ b/db/autocompact_test.cc
@@ -2,9 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
-#include "leveldb/db.h"
 #include "db/db_impl.h"
 #include "leveldb/cache.h"
+#include "leveldb/db.h"
 #include "util/testharness.h"
 #include "util/testutil.h"
 
@@ -12,11 +12,6 @@ namespace leveldb {
 
 class AutoCompactTest {
  public:
-  std::string dbname_;
-  Cache* tiny_cache_;
-  Options options_;
-  DB* db_;
-
   AutoCompactTest() {
     dbname_ = test::TmpDir() + "/autocompact_test";
     tiny_cache_ = NewLRUCache(100);
@@ -47,6 +42,12 @@ class AutoCompactTest {
   }
 
   void DoReads(int n);
+
+ private:
+  std::string dbname_;
+  Cache* tiny_cache_;
+  Options options_;
+  DB* db_;
 };
 
 static const int kValueSize = 200 * 1024;
@@ -81,17 +82,16 @@ void AutoCompactTest::DoReads(int n) {
     ASSERT_LT(read, 100) << "Taking too long to compact";
     Iterator* iter = db_->NewIterator(ReadOptions());
     for (iter->SeekToFirst();
-         iter->Valid() && iter->key().ToString() < limit_key;
-         iter->Next()) {
+         iter->Valid() && iter->key().ToString() < limit_key; iter->Next()) {
       // Drop data
     }
     delete iter;
     // Wait a little bit to allow any triggered compactions to complete.
     Env::Default()->SleepForMicroseconds(1000000);
     uint64_t size = Size(Key(0), Key(n));
-    fprintf(stderr, "iter %3d => %7.3f MB [other %7.3f MB]\n",
-            read+1, size/1048576.0, Size(Key(n), Key(kCount))/1048576.0);
-    if (size <= initial_size/10) {
+    fprintf(stderr, "iter %3d => %7.3f MB [other %7.3f MB]\n", read + 1,
+            size / 1048576.0, Size(Key(n), Key(kCount)) / 1048576.0);
+    if (size <= initial_size / 10) {
       break;
     }
   }
@@ -100,19 +100,13 @@ void AutoCompactTest::DoReads(int n) {
   // is pretty much unchanged.
   const int64_t final_other_size = Size(Key(n), Key(kCount));
   ASSERT_LE(final_other_size, initial_other_size + 1048576);
-  ASSERT_GE(final_other_size, initial_other_size/5 - 1048576);
+  ASSERT_GE(final_other_size, initial_other_size / 5 - 1048576);
 }
 
-TEST(AutoCompactTest, ReadAll) {
-  DoReads(kCount);
-}
+TEST(AutoCompactTest, ReadAll) { DoReads(kCount); }
 
-TEST(AutoCompactTest, ReadHalf) {
-  DoReads(kCount/2);
-}
+TEST(AutoCompactTest, ReadHalf) { DoReads(kCount / 2); }
 
 }  // namespace leveldb
 
-int main(int argc, char** argv) {
-  return leveldb::test::RunAllTests();
-}
+int main(int argc, char** argv) { return leveldb::test::RunAllTests(); }
diff --git a/db/builder.cc b/db/builder.cc
index f419882..9520ee4 100644
--- a/db/builder.cc
+++ b/db/builder.cc
@@ -4,8 +4,8 @@
 
 #include "db/builder.h"
 
-#include "db/filename.h"
 #include "db/dbformat.h"
+#include "db/filename.h"
 #include "db/table_cache.h"
 #include "db/version_edit.h"
 #include "leveldb/db.h"
@@ -14,12 +14,8 @@
 
 namespace leveldb {
 
-Status BuildTable(const std::string& dbname,
-                  Env* env,
-                  const Options& options,
-                  TableCache* table_cache,
-                  Iterator* iter,
-                  FileMetaData* meta) {
+Status BuildTable(const std::string& dbname, Env* env, const Options& options,
+                  TableCache* table_cache, Iterator* iter, FileMetaData* meta) {
   Status s;
   meta->file_size = 0;
   iter->SeekToFirst();
@@ -41,14 +37,10 @@ Status BuildTable(const std::string& dbname,
     }
 
     // Finish and check for builder errors
+    s = builder->Finish();
     if (s.ok()) {
-      s = builder->Finish();
-      if (s.ok()) {
-        meta->file_size = builder->FileSize();
-        assert(meta->file_size > 0);
-      }
-    } else {
-      builder->Abandon();
+      meta->file_size = builder->FileSize();
+      assert(meta->file_size > 0);
     }
     delete builder;
 
@@ -60,12 +52,11 @@ Status BuildTable(const std::string& dbname,
       s = file->Close();
     }
     delete file;
-    file = NULL;
+    file = nullptr;
 
     if (s.ok()) {
       // Verify that the table is usable
-      Iterator* it = table_cache->NewIterator(ReadOptions(),
-                                              meta->number,
+      Iterator* it = table_cache->NewIterator(ReadOptions(), meta->number,
                                               meta->file_size);
       s = it->status();
       delete it;
diff --git a/db/builder.h b/db/builder.h
index 62431fc..7bd0b80 100644
--- a/db/builder.h
+++ b/db/builder.h
@@ -22,12 +22,8 @@ class VersionEdit;
 // *meta will be filled with metadata about the generated table.
 // If no data is present in *iter, meta->file_size will be set to
 // zero, and no Table file will be produced.
-extern Status BuildTable(const std::string& dbname,
-                         Env* env,
-                         const Options& options,
-                         TableCache* table_cache,
-                         Iterator* iter,
-                         FileMetaData* meta);
+Status BuildTable(const std::string& dbname, Env* env, const Options& options,
+                  TableCache* table_cache, Iterator* iter, FileMetaData* meta);
 
 }  // namespace leveldb
 
diff --git a/db/c.cc b/db/c.cc
index 08ff0ad..1f6fd64 100644
--- a/db/c.cc
+++ b/db/c.cc
@@ -5,7 +5,7 @@
 #include "leveldb/c.h"
 
 #include <stdlib.h>
-#include <unistd.h>
+
 #include "leveldb/cache.h"
 #include "leveldb/comparator.h"
 #include "leveldb/db.h"
@@ -43,69 +43,72 @@ using leveldb::WriteOptions;
 
 extern "C" {
 
-struct leveldb_t              { DB*               rep; };
-struct leveldb_iterator_t     { Iterator*         rep; };
-struct leveldb_writebatch_t   { WriteBatch        rep; };
-struct leveldb_snapshot_t     { const Snapshot*   rep; };
-struct leveldb_readoptions_t  { ReadOptions       rep; };
-struct leveldb_writeoptions_t { WriteOptions      rep; };
-struct leveldb_options_t      { Options           rep; };
-struct leveldb_cache_t        { Cache*            rep; };
-struct leveldb_seqfile_t      { SequentialFile*   rep; };
-struct leveldb_randomfile_t   { RandomAccessFile* rep; };
-struct leveldb_writablefile_t { WritableFile*     rep; };
-struct leveldb_logger_t       { Logger*           rep; };
-struct leveldb_filelock_t     { FileLock*         rep; };
+struct leveldb_t {
+  DB* rep;
+};
+struct leveldb_iterator_t {
+  Iterator* rep;
+};
+struct leveldb_writebatch_t {
+  WriteBatch rep;
+};
+struct leveldb_snapshot_t {
+  const Snapshot* rep;
+};
+struct leveldb_readoptions_t {
+  ReadOptions rep;
+};
+struct leveldb_writeoptions_t {
+  WriteOptions rep;
+};
+struct leveldb_options_t {
+  Options rep;
+};
+struct leveldb_cache_t {
+  Cache* rep;
+};
+struct leveldb_seqfile_t {
+  SequentialFile* rep;
+};
+struct leveldb_randomfile_t {
+  RandomAccessFile* rep;
+};
+struct leveldb_writablefile_t {
+  WritableFile* rep;
+};
+struct leveldb_logger_t {
+  Logger* rep;
+};
+struct leveldb_filelock_t {
+  FileLock* rep;
+};
 
 struct leveldb_comparator_t : public Comparator {
-  void* state_;
-  void (*destructor_)(void*);
-  int (*compare_)(
-      void*,
-      const char* a, size_t alen,
-      const char* b, size_t blen);
-  const char* (*name_)(void*);
+  ~leveldb_comparator_t() override { (*destructor_)(state_); }
 
-  virtual ~leveldb_comparator_t() {
-    (*destructor_)(state_);
-  }
-
-  virtual int Compare(const Slice& a, const Slice& b) const {
+  int Compare(const Slice& a, const Slice& b) const override {
     return (*compare_)(state_, a.data(), a.size(), b.data(), b.size());
   }
 
-  virtual const char* Name() const {
-    return (*name_)(state_);
-  }
+  const char* Name() const override { return (*name_)(state_); }
 
   // No-ops since the C binding does not support key shortening methods.
-  virtual void FindShortestSeparator(std::string*, const Slice&) const { }
-  virtual void FindShortSuccessor(std::string* key) const { }
-};
+  void FindShortestSeparator(std::string*, const Slice&) const override {}
+  void FindShortSuccessor(std::string* key) const override {}
 
-struct leveldb_filterpolicy_t : public FilterPolicy {
   void* state_;
   void (*destructor_)(void*);
+  int (*compare_)(void*, const char* a, size_t alen, const char* b,
+                  size_t blen);
   const char* (*name_)(void*);
-  char* (*create_)(
-      void*,
-      const char* const* key_array, const size_t* key_length_array,
-      int num_keys,
-      size_t* filter_length);
-  unsigned char (*key_match_)(
-      void*,
-      const char* key, size_t length,
-      const char* filter, size_t filter_length);
-
-  virtual ~leveldb_filterpolicy_t() {
-    (*destructor_)(state_);
-  }
+};
 
-  virtual const char* Name() const {
-    return (*name_)(state_);
-  }
+struct leveldb_filterpolicy_t : public FilterPolicy {
+  ~leveldb_filterpolicy_t() override { (*destructor_)(state_); }
 
-  virtual void CreateFilter(const Slice* keys, int n, std::string* dst) const {
+  const char* Name() const override { return (*name_)(state_); }
+
+  void CreateFilter(const Slice* keys, int n, std::string* dst) const override {
     std::vector<const char*> key_pointers(n);
     std::vector<size_t> key_sizes(n);
     for (int i = 0; i < n; i++) {
@@ -118,10 +121,19 @@ struct leveldb_filterpolicy_t : public FilterPolicy {
     free(filter);
   }
 
-  virtual bool KeyMayMatch(const Slice& key, const Slice& filter) const {
-    return (*key_match_)(state_, key.data(), key.size(),
-                         filter.data(), filter.size());
+  bool KeyMayMatch(const Slice& key, const Slice& filter) const override {
+    return (*key_match_)(state_, key.data(), key.size(), filter.data(),
+                         filter.size());
   }
+
+  void* state_;
+  void (*destructor_)(void*);
+  const char* (*name_)(void*);
+  char* (*create_)(void*, const char* const* key_array,
+                   const size_t* key_length_array, int num_keys,
+                   size_t* filter_length);
+  unsigned char (*key_match_)(void*, const char* key, size_t length,
+                              const char* filter, size_t filter_length);
 };
 
 struct leveldb_env_t {
@@ -130,10 +142,10 @@ struct leveldb_env_t {
 };
 
 static bool SaveError(char** errptr, const Status& s) {
-  assert(errptr != NULL);
+  assert(errptr != nullptr);
   if (s.ok()) {
     return false;
-  } else if (*errptr == NULL) {
+  } else if (*errptr == nullptr) {
     *errptr = strdup(s.ToString().c_str());
   } else {
     // TODO(sanjay): Merge with existing error?
@@ -149,13 +161,11 @@ static char* CopyString(const std::string& str) {
   return result;
 }
 
-leveldb_t* leveldb_open(
-    const leveldb_options_t* options,
-    const char* name,
-    char** errptr) {
+leveldb_t* leveldb_open(const leveldb_options_t* options, const char* name,
+                        char** errptr) {
   DB* db;
   if (SaveError(errptr, DB::Open(options->rep, std::string(name), &db))) {
-    return NULL;
+    return nullptr;
   }
   leveldb_t* result = new leveldb_t;
   result->rep = db;
@@ -167,40 +177,27 @@ void leveldb_close(leveldb_t* db) {
   delete db;
 }
 
-void leveldb_put(
-    leveldb_t* db,
-    const leveldb_writeoptions_t* options,
-    const char* key, size_t keylen,
-    const char* val, size_t vallen,
-    char** errptr) {
+void leveldb_put(leveldb_t* db, const leveldb_writeoptions_t* options,
+                 const char* key, size_t keylen, const char* val, size_t vallen,
+                 char** errptr) {
   SaveError(errptr,
             db->rep->Put(options->rep, Slice(key, keylen), Slice(val, vallen)));
 }
 
-void leveldb_delete(
-    leveldb_t* db,
-    const leveldb_writeoptions_t* options,
-    const char* key, size_t keylen,
-    char** errptr) {
+void leveldb_delete(leveldb_t* db, const leveldb_writeoptions_t* options,
+                    const char* key, size_t keylen, char** errptr) {
   SaveError(errptr, db->rep->Delete(options->rep, Slice(key, keylen)));
 }
 
-
-void leveldb_write(
-    leveldb_t* db,
-    const leveldb_writeoptions_t* options,
-    leveldb_writebatch_t* batch,
-    char** errptr) {
+void leveldb_write(leveldb_t* db, const leveldb_writeoptions_t* options,
+                   leveldb_writebatch_t* batch, char** errptr) {
   SaveError(errptr, db->rep->Write(options->rep, &batch->rep));
 }
 
-char* leveldb_get(
-    leveldb_t* db,
-    const leveldb_readoptions_t* options,
-    const char* key, size_t keylen,
-    size_t* vallen,
-    char** errptr) {
-  char* result = NULL;
+char* leveldb_get(leveldb_t* db, const leveldb_readoptions_t* options,
+                  const char* key, size_t keylen, size_t* vallen,
+                  char** errptr) {
+  char* result = nullptr;
   std::string tmp;
   Status s = db->rep->Get(options->rep, Slice(key, keylen), &tmp);
   if (s.ok()) {
@@ -216,45 +213,40 @@ char* leveldb_get(
 }
 
 leveldb_iterator_t* leveldb_create_iterator(
-    leveldb_t* db,
-    const leveldb_readoptions_t* options) {
+    leveldb_t* db, const leveldb_readoptions_t* options) {
   leveldb_iterator_t* result = new leveldb_iterator_t;
   result->rep = db->rep->NewIterator(options->rep);
   return result;
 }
 
-const leveldb_snapshot_t* leveldb_create_snapshot(
-    leveldb_t* db) {
+const leveldb_snapshot_t* leveldb_create_snapshot(leveldb_t* db) {
   leveldb_snapshot_t* result = new leveldb_snapshot_t;
   result->rep = db->rep->GetSnapshot();
   return result;
 }
 
-void leveldb_release_snapshot(
-    leveldb_t* db,
-    const leveldb_snapshot_t* snapshot) {
+void leveldb_release_snapshot(leveldb_t* db,
+                              const leveldb_snapshot_t* snapshot) {
   db->rep->ReleaseSnapshot(snapshot->rep);
   delete snapshot;
 }
 
-char* leveldb_property_value(
-    leveldb_t* db,
-    const char* propname) {
+char* leveldb_property_value(leveldb_t* db, const char* propname) {
   std::string tmp;
   if (db->rep->GetProperty(Slice(propname), &tmp)) {
     // We use strdup() since we expect human readable output.
     return strdup(tmp.c_str());
   } else {
-    return NULL;
+    return nullptr;
   }
 }
 
-void leveldb_approximate_sizes(
-    leveldb_t* db,
-    int num_ranges,
-    const char* const* range_start_key, const size_t* range_start_key_len,
-    const char* const* range_limit_key, const size_t* range_limit_key_len,
-    uint64_t* sizes) {
+void leveldb_approximate_sizes(leveldb_t* db, int num_ranges,
+                               const char* const* range_start_key,
+                               const size_t* range_start_key_len,
+                               const char* const* range_limit_key,
+                               const size_t* range_limit_key_len,
+                               uint64_t* sizes) {
   Range* ranges = new Range[num_ranges];
   for (int i = 0; i < num_ranges; i++) {
     ranges[i].start = Slice(range_start_key[i], range_start_key_len[i]);
@@ -264,28 +256,23 @@ void leveldb_approximate_sizes(
   delete[] ranges;
 }
 
-void leveldb_compact_range(
-    leveldb_t* db,
-    const char* start_key, size_t start_key_len,
-    const char* limit_key, size_t limit_key_len) {
+void leveldb_compact_range(leveldb_t* db, const char* start_key,
+                           size_t start_key_len, const char* limit_key,
+                           size_t limit_key_len) {
   Slice a, b;
   db->rep->CompactRange(
-      // Pass NULL Slice if corresponding "const char*" is NULL
-      (start_key ? (a = Slice(start_key, start_key_len), &a) : NULL),
-      (limit_key ? (b = Slice(limit_key, limit_key_len), &b) : NULL));
+      // Pass null Slice if corresponding "const char*" is null
+      (start_key ? (a = Slice(start_key, start_key_len), &a) : nullptr),
+      (limit_key ? (b = Slice(limit_key, limit_key_len), &b) : nullptr));
 }
 
-void leveldb_destroy_db(
-    const leveldb_options_t* options,
-    const char* name,
-    char** errptr) {
+void leveldb_destroy_db(const leveldb_options_t* options, const char* name,
+                        char** errptr) {
   SaveError(errptr, DestroyDB(name, options->rep));
 }
 
-void leveldb_repair_db(
-    const leveldb_options_t* options,
-    const char* name,
-    char** errptr) {
+void leveldb_repair_db(const leveldb_options_t* options, const char* name,
+                       char** errptr) {
   SaveError(errptr, RepairDB(name, options->rep));
 }
 
@@ -310,13 +297,9 @@ void leveldb_iter_seek(leveldb_iterator_t* iter, const char* k, size_t klen) {
   iter->rep->Seek(Slice(k, klen));
 }
 
-void leveldb_iter_next(leveldb_iterator_t* iter) {
-  iter->rep->Next();
-}
+void leveldb_iter_next(leveldb_iterator_t* iter) { iter->rep->Next(); }
 
-void leveldb_iter_prev(leveldb_iterator_t* iter) {
-  iter->rep->Prev();
-}
+void leveldb_iter_prev(leveldb_iterator_t* iter) { iter->rep->Prev(); }
 
 const char* leveldb_iter_key(const leveldb_iterator_t* iter, size_t* klen) {
   Slice s = iter->rep->key();
@@ -338,41 +321,34 @@ leveldb_writebatch_t* leveldb_writebatch_create() {
   return new leveldb_writebatch_t;
 }
 
-void leveldb_writebatch_destroy(leveldb_writebatch_t* b) {
-  delete b;
-}
+void leveldb_writebatch_destroy(leveldb_writebatch_t* b) { delete b; }
 
-void leveldb_writebatch_clear(leveldb_writebatch_t* b) {
-  b->rep.Clear();
-}
+void leveldb_writebatch_clear(leveldb_writebatch_t* b) { b->rep.Clear(); }
 
-void leveldb_writebatch_put(
-    leveldb_writebatch_t* b,
-    const char* key, size_t klen,
-    const char* val, size_t vlen) {
+void leveldb_writebatch_put(leveldb_writebatch_t* b, const char* key,
+                            size_t klen, const char* val, size_t vlen) {
   b->rep.Put(Slice(key, klen), Slice(val, vlen));
 }
 
-void leveldb_writebatch_delete(
-    leveldb_writebatch_t* b,
-    const char* key, size_t klen) {
+void leveldb_writebatch_delete(leveldb_writebatch_t* b, const char* key,
+                               size_t klen) {
   b->rep.Delete(Slice(key, klen));
 }
 
-void leveldb_writebatch_iterate(
-    leveldb_writebatch_t* b,
-    void* state,
-    void (*put)(void*, const char* k, size_t klen, const char* v, size_t vlen),
-    void (*deleted)(void*, const char* k, size_t klen)) {
+void leveldb_writebatch_iterate(const leveldb_writebatch_t* b, void* state,
+                                void (*put)(void*, const char* k, size_t klen,
+                                            const char* v, size_t vlen),
+                                void (*deleted)(void*, const char* k,
+                                                size_t klen)) {
   class H : public WriteBatch::Handler {
    public:
     void* state_;
     void (*put_)(void*, const char* k, size_t klen, const char* v, size_t vlen);
     void (*deleted_)(void*, const char* k, size_t klen);
-    virtual void Put(const Slice& key, const Slice& value) {
+    void Put(const Slice& key, const Slice& value) override {
       (*put_)(state_, key.data(), key.size(), value.data(), value.size());
     }
-    virtual void Delete(const Slice& key) {
+    void Delete(const Slice& key) override {
       (*deleted_)(state_, key.data(), key.size());
     }
   };
@@ -383,47 +359,46 @@ void leveldb_writebatch_iterate(
   b->rep.Iterate(&handler);
 }
 
-leveldb_options_t* leveldb_options_create() {
-  return new leveldb_options_t;
+void leveldb_writebatch_append(leveldb_writebatch_t* destination,
+                               const leveldb_writebatch_t* source) {
+  destination->rep.Append(source->rep);
 }
 
-void leveldb_options_destroy(leveldb_options_t* options) {
-  delete options;
-}
+leveldb_options_t* leveldb_options_create() { return new leveldb_options_t; }
+
+void leveldb_options_destroy(leveldb_options_t* options) { delete options; }
 
-void leveldb_options_set_comparator(
-    leveldb_options_t* opt,
-    leveldb_comparator_t* cmp) {
+void leveldb_options_set_comparator(leveldb_options_t* opt,
+                                    leveldb_comparator_t* cmp) {
   opt->rep.comparator = cmp;
 }
 
-void leveldb_options_set_filter_policy(
-    leveldb_options_t* opt,
-    leveldb_filterpolicy_t* policy) {
+void leveldb_options_set_filter_policy(leveldb_options_t* opt,
+                                       leveldb_filterpolicy_t* policy) {
   opt->rep.filter_policy = policy;
 }
 
-void leveldb_options_set_create_if_missing(
-    leveldb_options_t* opt, unsigned char v) {
+void leveldb_options_set_create_if_missing(leveldb_options_t* opt,
+                                           unsigned char v) {
   opt->rep.create_if_missing = v;
 }
 
-void leveldb_options_set_error_if_exists(
-    leveldb_options_t* opt, unsigned char v) {
+void leveldb_options_set_error_if_exists(leveldb_options_t* opt,
+                                         unsigned char v) {
   opt->rep.error_if_exists = v;
 }
 
-void leveldb_options_set_paranoid_checks(
-    leveldb_options_t* opt, unsigned char v) {
+void leveldb_options_set_paranoid_checks(leveldb_options_t* opt,
+                                         unsigned char v) {
   opt->rep.paranoid_checks = v;
 }
 
 void leveldb_options_set_env(leveldb_options_t* opt, leveldb_env_t* env) {
-  opt->rep.env = (env ? env->rep : NULL);
+  opt->rep.env = (env ? env->rep : nullptr);
 }
 
 void leveldb_options_set_info_log(leveldb_options_t* opt, leveldb_logger_t* l) {
-  opt->rep.info_log = (l ? l->rep : NULL);
+  opt->rep.info_log = (l ? l->rep : nullptr);
 }
 
 void leveldb_options_set_write_buffer_size(leveldb_options_t* opt, size_t s) {
@@ -446,17 +421,18 @@ void leveldb_options_set_block_restart_interval(leveldb_options_t* opt, int n) {
   opt->rep.block_restart_interval = n;
 }
 
+void leveldb_options_set_max_file_size(leveldb_options_t* opt, size_t s) {
+  opt->rep.max_file_size = s;
+}
+
 void leveldb_options_set_compression(leveldb_options_t* opt, int t) {
   opt->rep.compression = static_cast<CompressionType>(t);
 }
 
 leveldb_comparator_t* leveldb_comparator_create(
-    void* state,
-    void (*destructor)(void*),
-    int (*compare)(
-        void*,
-        const char* a, size_t alen,
-        const char* b, size_t blen),
+    void* state, void (*destructor)(void*),
+    int (*compare)(void*, const char* a, size_t alen, const char* b,
+                   size_t blen),
     const char* (*name)(void*)) {
   leveldb_comparator_t* result = new leveldb_comparator_t;
   result->state_ = state;
@@ -466,22 +442,15 @@ leveldb_comparator_t* leveldb_comparator_create(
   return result;
 }
 
-void leveldb_comparator_destroy(leveldb_comparator_t* cmp) {
-  delete cmp;
-}
+void leveldb_comparator_destroy(leveldb_comparator_t* cmp) { delete cmp; }
 
 leveldb_filterpolicy_t* leveldb_filterpolicy_create(
-    void* state,
-    void (*destructor)(void*),
-    char* (*create_filter)(
-        void*,
-        const char* const* key_array, const size_t* key_length_array,
-        int num_keys,
-        size_t* filter_length),
-    unsigned char (*key_may_match)(
-        void*,
-        const char* key, size_t length,
-        const char* filter, size_t filter_length),
+    void* state, void (*destructor)(void*),
+    char* (*create_filter)(void*, const char* const* key_array,
+                           const size_t* key_length_array, int num_keys,
+                           size_t* filter_length),
+    unsigned char (*key_may_match)(void*, const char* key, size_t length,
+                                   const char* filter, size_t filter_length),
     const char* (*name)(void*)) {
   leveldb_filterpolicy_t* result = new leveldb_filterpolicy_t;
   result->state_ = state;
@@ -501,7 +470,8 @@ leveldb_filterpolicy_t* leveldb_filterpolicy_create_bloom(int bits_per_key) {
   // they delegate to a NewBloomFilterPolicy() instead of user
   // supplied C functions.
   struct Wrapper : public leveldb_filterpolicy_t {
-    const FilterPolicy* rep_;
+    static void DoNothing(void*) {}
+
     ~Wrapper() { delete rep_; }
     const char* Name() const { return rep_->Name(); }
     void CreateFilter(const Slice* keys, int n, std::string* dst) const {
@@ -510,11 +480,12 @@ leveldb_filterpolicy_t* leveldb_filterpolicy_create_bloom(int bits_per_key) {
     bool KeyMayMatch(const Slice& key, const Slice& filter) const {
       return rep_->KeyMayMatch(key, filter);
     }
-    static void DoNothing(void*) { }
+
+    const FilterPolicy* rep_;
   };
   Wrapper* wrapper = new Wrapper;
   wrapper->rep_ = NewBloomFilterPolicy(bits_per_key);
-  wrapper->state_ = NULL;
+  wrapper->state_ = nullptr;
   wrapper->destructor_ = &Wrapper::DoNothing;
   return wrapper;
 }
@@ -523,37 +494,31 @@ leveldb_readoptions_t* leveldb_readoptions_create() {
   return new leveldb_readoptions_t;
 }
 
-void leveldb_readoptions_destroy(leveldb_readoptions_t* opt) {
-  delete opt;
-}
+void leveldb_readoptions_destroy(leveldb_readoptions_t* opt) { delete opt; }
 
-void leveldb_readoptions_set_verify_checksums(
-    leveldb_readoptions_t* opt,
-    unsigned char v) {
+void leveldb_readoptions_set_verify_checksums(leveldb_readoptions_t* opt,
+                                              unsigned char v) {
   opt->rep.verify_checksums = v;
 }
 
-void leveldb_readoptions_set_fill_cache(
-    leveldb_readoptions_t* opt, unsigned char v) {
+void leveldb_readoptions_set_fill_cache(leveldb_readoptions_t* opt,
+                                        unsigned char v) {
   opt->rep.fill_cache = v;
 }
 
-void leveldb_readoptions_set_snapshot(
-    leveldb_readoptions_t* opt,
-    const leveldb_snapshot_t* snap) {
-  opt->rep.snapshot = (snap ? snap->rep : NULL);
+void leveldb_readoptions_set_snapshot(leveldb_readoptions_t* opt,
+                                      const leveldb_snapshot_t* snap) {
+  opt->rep.snapshot = (snap ? snap->rep : nullptr);
 }
 
 leveldb_writeoptions_t* leveldb_writeoptions_create() {
   return new leveldb_writeoptions_t;
 }
 
-void leveldb_writeoptions_destroy(leveldb_writeoptions_t* opt) {
-  delete opt;
-}
+void leveldb_writeoptions_destroy(leveldb_writeoptions_t* opt) { delete opt; }
 
-void leveldb_writeoptions_set_sync(
-    leveldb_writeoptions_t* opt, unsigned char v) {
+void leveldb_writeoptions_set_sync(leveldb_writeoptions_t* opt,
+                                   unsigned char v) {
   opt->rep.sync = v;
 }
 
@@ -580,16 +545,22 @@ void leveldb_env_destroy(leveldb_env_t* env) {
   delete env;
 }
 
-void leveldb_free(void* ptr) {
-  free(ptr);
-}
+char* leveldb_env_get_test_directory(leveldb_env_t* env) {
+  std::string result;
+  if (!env->rep->GetTestDirectory(&result).ok()) {
+    return nullptr;
+  }
 
-int leveldb_major_version() {
-  return kMajorVersion;
+  char* buffer = static_cast<char*>(malloc(result.size() + 1));
+  memcpy(buffer, result.data(), result.size());
+  buffer[result.size()] = '\0';
+  return buffer;
 }
 
-int leveldb_minor_version() {
-  return kMinorVersion;
-}
+void leveldb_free(void* ptr) { free(ptr); }
+
+int leveldb_major_version() { return kMajorVersion; }
+
+int leveldb_minor_version() { return kMinorVersion; }
 
 }  // end extern "C"
diff --git a/db/c_test.c b/db/c_test.c
index 7cd5ee0..ae14b99 100644
--- a/db/c_test.c
+++ b/db/c_test.c
@@ -8,24 +8,14 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sys/types.h>
-#include <unistd.h>
 
 const char* phase = "";
-static char dbname[200];
 
 static void StartPhase(const char* name) {
   fprintf(stderr, "=== Test %s\n", name);
   phase = name;
 }
 
-static const char* GetTempDir(void) {
-    const char* ret = getenv("TEST_TMPDIR");
-    if (ret == NULL || ret[0] == '\0')
-        ret = "/tmp";
-    return ret;
-}
-
 #define CheckNoError(err)                                               \
   if ((err) != NULL) {                                                  \
     fprintf(stderr, "%s:%d: %s: %s\n", __FILE__, __LINE__, phase, (err)); \
@@ -162,21 +152,19 @@ int main(int argc, char** argv) {
   leveldb_options_t* options;
   leveldb_readoptions_t* roptions;
   leveldb_writeoptions_t* woptions;
+  char* dbname;
   char* err = NULL;
   int run = -1;
 
   CheckCondition(leveldb_major_version() >= 1);
   CheckCondition(leveldb_minor_version() >= 1);
 
-  snprintf(dbname, sizeof(dbname),
-           "%s/leveldb_c_test-%d",
-           GetTempDir(),
-           ((int) geteuid()));
-
   StartPhase("create_objects");
   cmp = leveldb_comparator_create(NULL, CmpDestroy, CmpCompare, CmpName);
   env = leveldb_create_default_env();
   cache = leveldb_cache_create_lru(100000);
+  dbname = leveldb_env_get_test_directory(env);
+  CheckCondition(dbname != NULL);
 
   options = leveldb_options_create();
   leveldb_options_set_comparator(options, cmp);
@@ -189,6 +177,7 @@ int main(int argc, char** argv) {
   leveldb_options_set_max_open_files(options, 10);
   leveldb_options_set_block_size(options, 1024);
   leveldb_options_set_block_restart_interval(options, 8);
+  leveldb_options_set_max_file_size(options, 3 << 20);
   leveldb_options_set_compression(options, leveldb_no_compression);
 
   roptions = leveldb_readoptions_create();
@@ -239,12 +228,18 @@ int main(int argc, char** argv) {
     leveldb_writebatch_clear(wb);
     leveldb_writebatch_put(wb, "bar", 3, "b", 1);
     leveldb_writebatch_put(wb, "box", 3, "c", 1);
-    leveldb_writebatch_delete(wb, "bar", 3);
+
+    leveldb_writebatch_t* wb2 = leveldb_writebatch_create();
+    leveldb_writebatch_delete(wb2, "bar", 3);
+    leveldb_writebatch_append(wb, wb2);
+    leveldb_writebatch_destroy(wb2);
+
     leveldb_write(db, woptions, wb, &err);
     CheckNoError(err);
     CheckGet(db, roptions, "foo", "hello");
     CheckGet(db, roptions, "bar", NULL);
     CheckGet(db, roptions, "box", "c");
+
     int pos = 0;
     leveldb_writebatch_iterate(wb, &pos, CheckPut, CheckDel);
     CheckCondition(pos == 3);
@@ -381,6 +376,7 @@ int main(int argc, char** argv) {
   leveldb_options_destroy(options);
   leveldb_readoptions_destroy(roptions);
   leveldb_writeoptions_destroy(woptions);
+  leveldb_free(dbname);
   leveldb_cache_destroy(cache);
   leveldb_comparator_destroy(cmp);
   leveldb_env_destroy(env);
diff --git a/db/corruption_test.cc b/db/corruption_test.cc
index 96afc68..42f5237 100644
--- a/db/corruption_test.cc
+++ b/db/corruption_test.cc
@@ -2,20 +2,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
-#include "leveldb/db.h"
-
-#include <errno.h>
-#include <fcntl.h>
-#include <sys/stat.h>
 #include <sys/types.h>
-#include "leveldb/cache.h"
-#include "leveldb/env.h"
-#include "leveldb/table.h"
-#include "leveldb/write_batch.h"
+
 #include "db/db_impl.h"
 #include "db/filename.h"
 #include "db/log_format.h"
 #include "db/version_set.h"
+#include "leveldb/cache.h"
+#include "leveldb/db.h"
+#include "leveldb/table.h"
+#include "leveldb/write_batch.h"
 #include "util/logging.h"
 #include "util/testharness.h"
 #include "util/testutil.h"
@@ -26,44 +22,35 @@ static const int kValueSize = 1000;
 
 class CorruptionTest {
  public:
-  test::ErrorEnv env_;
-  std::string dbname_;
-  Cache* tiny_cache_;
-  Options options_;
-  DB* db_;
-
-  CorruptionTest() {
-    tiny_cache_ = NewLRUCache(100);
+  CorruptionTest()
+      : db_(nullptr),
+        dbname_("/memenv/corruption_test"),
+        tiny_cache_(NewLRUCache(100)) {
     options_.env = &env_;
     options_.block_cache = tiny_cache_;
-    dbname_ = test::TmpDir() + "/db_test";
     DestroyDB(dbname_, options_);
 
-    db_ = NULL;
     options_.create_if_missing = true;
     Reopen();
     options_.create_if_missing = false;
   }
 
   ~CorruptionTest() {
-     delete db_;
-     DestroyDB(dbname_, Options());
-     delete tiny_cache_;
+    delete db_;
+    delete tiny_cache_;
   }
 
   Status TryReopen() {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
     return DB::Open(options_, dbname_, &db_);
   }
 
-  void Reopen() {
-    ASSERT_OK(TryReopen());
-  }
+  void Reopen() { ASSERT_OK(TryReopen()); }
 
   void RepairDB() {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
     ASSERT_OK(::leveldb::RepairDB(dbname_, options_));
   }
 
@@ -71,7 +58,7 @@ class CorruptionTest {
     std::string key_space, value_space;
     WriteBatch batch;
     for (int i = 0; i < n; i++) {
-      //if ((i % 100) == 0) fprintf(stderr, "@ %d of %d\n", i, n);
+      // if ((i % 100) == 0) fprintf(stderr, "@ %d of %d\n", i, n);
       Slice key = Key(i, &key_space);
       batch.Clear();
       batch.Put(key, Value(i, &value_space));
@@ -100,8 +87,7 @@ class CorruptionTest {
         // Ignore boundary keys.
         continue;
       }
-      if (!ConsumeDecimalNumber(&in, &key) ||
-          !in.empty() ||
+      if (!ConsumeDecimalNumber(&in, &key) || !in.empty() ||
           key < next_expected) {
         bad_keys++;
         continue;
@@ -126,14 +112,13 @@ class CorruptionTest {
   void Corrupt(FileType filetype, int offset, int bytes_to_corrupt) {
     // Pick file to corrupt
     std::vector<std::string> filenames;
-    ASSERT_OK(env_.GetChildren(dbname_, &filenames));
+    ASSERT_OK(env_.target()->GetChildren(dbname_, &filenames));
     uint64_t number;
     FileType type;
     std::string fname;
     int picked_number = -1;
     for (size_t i = 0; i < filenames.size(); i++) {
-      if (ParseFileName(filenames[i], &number, &type) &&
-          type == filetype &&
+      if (ParseFileName(filenames[i], &number, &type) && type == filetype &&
           int(number) > picked_number) {  // Pick latest file
         fname = dbname_ + "/" + filenames[i];
         picked_number = number;
@@ -141,35 +126,32 @@ class CorruptionTest {
     }
     ASSERT_TRUE(!fname.empty()) << filetype;
 
-    struct stat sbuf;
-    if (stat(fname.c_str(), &sbuf) != 0) {
-      const char* msg = strerror(errno);
-      ASSERT_TRUE(false) << fname << ": " << msg;
-    }
+    uint64_t file_size;
+    ASSERT_OK(env_.target()->GetFileSize(fname, &file_size));
 
     if (offset < 0) {
       // Relative to end of file; make it absolute
-      if (-offset > sbuf.st_size) {
+      if (-offset > file_size) {
         offset = 0;
       } else {
-        offset = sbuf.st_size + offset;
+        offset = file_size + offset;
       }
     }
-    if (offset > sbuf.st_size) {
-      offset = sbuf.st_size;
+    if (offset > file_size) {
+      offset = file_size;
     }
-    if (offset + bytes_to_corrupt > sbuf.st_size) {
-      bytes_to_corrupt = sbuf.st_size - offset;
+    if (offset + bytes_to_corrupt > file_size) {
+      bytes_to_corrupt = file_size - offset;
     }
 
     // Do it
     std::string contents;
-    Status s = ReadFileToString(Env::Default(), fname, &contents);
+    Status s = ReadFileToString(env_.target(), fname, &contents);
     ASSERT_TRUE(s.ok()) << s.ToString();
     for (int i = 0; i < bytes_to_corrupt; i++) {
       contents[i + offset] ^= 0x80;
     }
-    s = WriteStringToFile(Env::Default(), contents, fname);
+    s = WriteStringToFile(env_.target(), contents, fname);
     ASSERT_TRUE(s.ok()) << s.ToString();
   }
 
@@ -197,12 +179,20 @@ class CorruptionTest {
     Random r(k);
     return test::RandomString(&r, kValueSize, storage);
   }
+
+  test::ErrorEnv env_;
+  Options options_;
+  DB* db_;
+
+ private:
+  std::string dbname_;
+  Cache* tiny_cache_;
 };
 
 TEST(CorruptionTest, Recovery) {
   Build(100);
   Check(100, 100);
-  Corrupt(kLogFile, 19, 1);      // WriteBatch tag for first record
+  Corrupt(kLogFile, 19, 1);  // WriteBatch tag for first record
   Corrupt(kLogFile, log::kBlockSize + 1000, 1);  // Somewhere in second block
   Reopen();
 
@@ -237,8 +227,8 @@ TEST(CorruptionTest, TableFile) {
   Build(100);
   DBImpl* dbi = reinterpret_cast<DBImpl*>(db_);
   dbi->TEST_CompactMemTable();
-  dbi->TEST_CompactRange(0, NULL, NULL);
-  dbi->TEST_CompactRange(1, NULL, NULL);
+  dbi->TEST_CompactRange(0, nullptr, nullptr);
+  dbi->TEST_CompactRange(1, nullptr, nullptr);
 
   Corrupt(kTableFile, 100, 1);
   Check(90, 99);
@@ -251,8 +241,8 @@ TEST(CorruptionTest, TableFileRepair) {
   Build(100);
   DBImpl* dbi = reinterpret_cast<DBImpl*>(db_);
   dbi->TEST_CompactMemTable();
-  dbi->TEST_CompactRange(0, NULL, NULL);
-  dbi->TEST_CompactRange(1, NULL, NULL);
+  dbi->TEST_CompactRange(0, nullptr, nullptr);
+  dbi->TEST_CompactRange(1, nullptr, nullptr);
 
   Corrupt(kTableFile, 100, 1);
   RepairDB();
@@ -302,7 +292,7 @@ TEST(CorruptionTest, CorruptedDescriptor) {
   ASSERT_OK(db_->Put(WriteOptions(), "foo", "hello"));
   DBImpl* dbi = reinterpret_cast<DBImpl*>(db_);
   dbi->TEST_CompactMemTable();
-  dbi->TEST_CompactRange(0, NULL, NULL);
+  dbi->TEST_CompactRange(0, nullptr, nullptr);
 
   Corrupt(kDescriptorFile, 0, 1000);
   Status s = TryReopen();
@@ -343,7 +333,7 @@ TEST(CorruptionTest, CompactionInputErrorParanoid) {
     Corrupt(kTableFile, 100, 1);
     env_.SleepForMicroseconds(100000);
   }
-  dbi->CompactRange(NULL, NULL);
+  dbi->CompactRange(nullptr, nullptr);
 
   // Write must fail because of corrupted table
   std::string tmp1, tmp2;
@@ -369,6 +359,4 @@ TEST(CorruptionTest, UnrelatedKeys) {
 
 }  // namespace leveldb
 
-int main(int argc, char** argv) {
-  return leveldb::test::RunAllTests();
-}
+int main(int argc, char** argv) { return leveldb::test::RunAllTests(); }
diff --git a/db/db_bench.cc b/db/db_bench.cc
deleted file mode 100644
index e5975bd..0000000
--- a/db/db_bench.cc
+++ /dev/null
@@ -1,991 +0,0 @@
-// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file. See the AUTHORS file for names of contributors.
-
-#include <sys/types.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include "db/db_impl.h"
-#include "db/version_set.h"
-#include "leveldb/cache.h"
-#include "leveldb/db.h"
-#include "leveldb/env.h"
-#include "leveldb/write_batch.h"
-#include "port/port.h"
-#include "util/crc32c.h"
-#include "util/histogram.h"
-#include "util/mutexlock.h"
-#include "util/random.h"
-#include "util/testutil.h"
-
-// Comma-separated list of operations to run in the specified order
-//   Actual benchmarks:
-//      fillseq       -- write N values in sequential key order in async mode
-//      fillrandom    -- write N values in random key order in async mode
-//      overwrite     -- overwrite N values in random key order in async mode
-//      fillsync      -- write N/100 values in random key order in sync mode
-//      fill100K      -- write N/1000 100K values in random order in async mode
-//      deleteseq     -- delete N keys in sequential order
-//      deleterandom  -- delete N keys in random order
-//      readseq       -- read N times sequentially
-//      readreverse   -- read N times in reverse order
-//      readrandom    -- read N times in random order
-//      readmissing   -- read N missing keys in random order
-//      readhot       -- read N times in random order from 1% section of DB
-//      seekrandom    -- N random seeks
-//      open          -- cost of opening a DB
-//      crc32c        -- repeated crc32c of 4K of data
-//      acquireload   -- load N*1000 times
-//   Meta operations:
-//      compact     -- Compact the entire DB
-//      stats       -- Print DB stats
-//      sstables    -- Print sstable info
-//      heapprofile -- Dump a heap profile (if supported by this port)
-static const char* FLAGS_benchmarks =
-    "fillseq,"
-    "fillsync,"
-    "fillrandom,"
-    "overwrite,"
-    "readrandom,"
-    "readrandom,"  // Extra run to allow previous compactions to quiesce
-    "readseq,"
-    "readreverse,"
-    "compact,"
-    "readrandom,"
-    "readseq,"
-    "readreverse,"
-    "fill100K,"
-    "crc32c,"
-    "snappycomp,"
-    "snappyuncomp,"
-    "acquireload,"
-    ;
-
-// Number of key/values to place in database
-static int FLAGS_num = 1000000;
-
-// Number of read operations to do.  If negative, do FLAGS_num reads.
-static int FLAGS_reads = -1;
-
-// Number of concurrent threads to run.
-static int FLAGS_threads = 1;
-
-// Size of each value
-static int FLAGS_value_size = 100;
-
-// Arrange to generate values that shrink to this fraction of
-// their original size after compression
-static double FLAGS_compression_ratio = 0.5;
-
-// Print histogram of operation timings
-static bool FLAGS_histogram = false;
-
-// Number of bytes to buffer in memtable before compacting
-// (initialized to default value by "main")
-static int FLAGS_write_buffer_size = 0;
-
-// Number of bytes to use as a cache of uncompressed data.
-// Negative means use default settings.
-static int FLAGS_cache_size = -1;
-
-// Maximum number of files to keep open at the same time (use default if == 0)
-static int FLAGS_open_files = 0;
-
-// Bloom filter bits per key.
-// Negative means use default settings.
-static int FLAGS_bloom_bits = -1;
-
-// If true, do not destroy the existing database.  If you set this
-// flag and also specify a benchmark that wants a fresh database, that
-// benchmark will fail.
-static bool FLAGS_use_existing_db = false;
-
-// Use the db with the following name.
-static const char* FLAGS_db = NULL;
-
-namespace leveldb {
-
-namespace {
-
-// Helper for quickly generating random data.
-class RandomGenerator {
- private:
-  std::string data_;
-  int pos_;
-
- public:
-  RandomGenerator() {
-    // We use a limited amount of data over and over again and ensure
-    // that it is larger than the compression window (32KB), and also
-    // large enough to serve all typical value sizes we want to write.
-    Random rnd(301);
-    std::string piece;
-    while (data_.size() < 1048576) {
-      // Add a short fragment that is as compressible as specified
-      // by FLAGS_compression_ratio.
-      test::CompressibleString(&rnd, FLAGS_compression_ratio, 100, &piece);
-      data_.append(piece);
-    }
-    pos_ = 0;
-  }
-
-  Slice Generate(size_t len) {
-    if (pos_ + len > data_.size()) {
-      pos_ = 0;
-      assert(len < data_.size());
-    }
-    pos_ += len;
-    return Slice(data_.data() + pos_ - len, len);
-  }
-};
-
-static Slice TrimSpace(Slice s) {
-  size_t start = 0;
-  while (start < s.size() && isspace(s[start])) {
-    start++;
-  }
-  size_t limit = s.size();
-  while (limit > start && isspace(s[limit-1])) {
-    limit--;
-  }
-  return Slice(s.data() + start, limit - start);
-}
-
-static void AppendWithSpace(std::string* str, Slice msg) {
-  if (msg.empty()) return;
-  if (!str->empty()) {
-    str->push_back(' ');
-  }
-  str->append(msg.data(), msg.size());
-}
-
-class Stats {
- private:
-  double start_;
-  double finish_;
-  double seconds_;
-  int done_;
-  int next_report_;
-  int64_t bytes_;
-  double last_op_finish_;
-  Histogram hist_;
-  std::string message_;
-
- public:
-  Stats() { Start(); }
-
-  void Start() {
-    next_report_ = 100;
-    last_op_finish_ = start_;
-    hist_.Clear();
-    done_ = 0;
-    bytes_ = 0;
-    seconds_ = 0;
-    start_ = Env::Default()->NowMicros();
-    finish_ = start_;
-    message_.clear();
-  }
-
-  void Merge(const Stats& other) {
-    hist_.Merge(other.hist_);
-    done_ += other.done_;
-    bytes_ += other.bytes_;
-    seconds_ += other.seconds_;
-    if (other.start_ < start_) start_ = other.start_;
-    if (other.finish_ > finish_) finish_ = other.finish_;
-
-    // Just keep the messages from one thread
-    if (message_.empty()) message_ = other.message_;
-  }
-
-  void Stop() {
-    finish_ = Env::Default()->NowMicros();
-    seconds_ = (finish_ - start_) * 1e-6;
-  }
-
-  void AddMessage(Slice msg) {
-    AppendWithSpace(&message_, msg);
-  }
-
-  void FinishedSingleOp() {
-    if (FLAGS_histogram) {
-      double now = Env::Default()->NowMicros();
-      double micros = now - last_op_finish_;
-      hist_.Add(micros);
-      if (micros > 20000) {
-        fprintf(stderr, "long op: %.1f micros%30s\r", micros, "");
-        fflush(stderr);
-      }
-      last_op_finish_ = now;
-    }
-
-    done_++;
-    if (done_ >= next_report_) {
-      if      (next_report_ < 1000)   next_report_ += 100;
-      else if (next_report_ < 5000)   next_report_ += 500;
-      else if (next_report_ < 10000)  next_report_ += 1000;
-      else if (next_report_ < 50000)  next_report_ += 5000;
-      else if (next_report_ < 100000) next_report_ += 10000;
-      else if (next_report_ < 500000) next_report_ += 50000;
-      else                            next_report_ += 100000;
-      fprintf(stderr, "... finished %d ops%30s\r", done_, "");
-      fflush(stderr);
-    }
-  }
-
-  void AddBytes(int64_t n) {
-    bytes_ += n;
-  }
-
-  void Report(const Slice& name) {
-    // Pretend at least one op was done in case we are running a benchmark
-    // that does not call FinishedSingleOp().
-    if (done_ < 1) done_ = 1;
-
-    std::string extra;
-    if (bytes_ > 0) {
-      // Rate is computed on actual elapsed time, not the sum of per-thread
-      // elapsed times.
-      double elapsed = (finish_ - start_) * 1e-6;
-      char rate[100];
-      snprintf(rate, sizeof(rate), "%6.1f MB/s",
-               (bytes_ / 1048576.0) / elapsed);
-      extra = rate;
-    }
-    AppendWithSpace(&extra, message_);
-
-    fprintf(stdout, "%-12s : %11.3f micros/op;%s%s\n",
-            name.ToString().c_str(),
-            seconds_ * 1e6 / done_,
-            (extra.empty() ? "" : " "),
-            extra.c_str());
-    if (FLAGS_histogram) {
-      fprintf(stdout, "Microseconds per op:\n%s\n", hist_.ToString().c_str());
-    }
-    fflush(stdout);
-  }
-};
-
-// State shared by all concurrent executions of the same benchmark.
-struct SharedState {
-  port::Mutex mu;
-  port::CondVar cv;
-  int total;
-
-  // Each thread goes through the following states:
-  //    (1) initializing
-  //    (2) waiting for others to be initialized
-  //    (3) running
-  //    (4) done
-
-  int num_initialized;
-  int num_done;
-  bool start;
-
-  SharedState() : cv(&mu) { }
-};
-
-// Per-thread state for concurrent executions of the same benchmark.
-struct ThreadState {
-  int tid;             // 0..n-1 when running in n threads
-  Random rand;         // Has different seeds for different threads
-  Stats stats;
-  SharedState* shared;
-
-  ThreadState(int index)
-      : tid(index),
-        rand(1000 + index) {
-  }
-};
-
-}  // namespace
-
-class Benchmark {
- private:
-  Cache* cache_;
-  const FilterPolicy* filter_policy_;
-  DB* db_;
-  int num_;
-  int value_size_;
-  int entries_per_batch_;
-  WriteOptions write_options_;
-  int reads_;
-  int heap_counter_;
-
-  void PrintHeader() {
-    const int kKeySize = 16;
-    PrintEnvironment();
-    fprintf(stdout, "Keys:       %d bytes each\n", kKeySize);
-    fprintf(stdout, "Values:     %d bytes each (%d bytes after compression)\n",
-            FLAGS_value_size,
-            static_cast<int>(FLAGS_value_size * FLAGS_compression_ratio + 0.5));
-    fprintf(stdout, "Entries:    %d\n", num_);
-    fprintf(stdout, "RawSize:    %.1f MB (estimated)\n",
-            ((static_cast<int64_t>(kKeySize + FLAGS_value_size) * num_)
-             / 1048576.0));
-    fprintf(stdout, "FileSize:   %.1f MB (estimated)\n",
-            (((kKeySize + FLAGS_value_size * FLAGS_compression_ratio) * num_)
-             / 1048576.0));
-    PrintWarnings();
-    fprintf(stdout, "------------------------------------------------\n");
-  }
-
-  void PrintWarnings() {
-#if defined(__GNUC__) && !defined(__OPTIMIZE__)
-    fprintf(stdout,
-            "WARNING: Optimization is disabled: benchmarks unnecessarily slow\n"
-            );
-#endif
-#ifndef NDEBUG
-    fprintf(stdout,
-            "WARNING: Assertions are enabled; benchmarks unnecessarily slow\n");
-#endif
-
-    // See if snappy is working by attempting to compress a compressible string
-    const char text[] = "yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy";
-    std::string compressed;
-    if (!port::Snappy_Compress(text, sizeof(text), &compressed)) {
-      fprintf(stdout, "WARNING: Snappy compression is not enabled\n");
-    } else if (compressed.size() >= sizeof(text)) {
-      fprintf(stdout, "WARNING: Snappy compression is not effective\n");
-    }
-  }
-
-  void PrintEnvironment() {
-    fprintf(stderr, "LevelDB:    version %d.%d\n",
-            kMajorVersion, kMinorVersion);
-
-#if defined(__linux)
-    time_t now = time(NULL);
-    fprintf(stderr, "Date:       %s", ctime(&now));  // ctime() adds newline
-
-    FILE* cpuinfo = fopen("/proc/cpuinfo", "r");
-    if (cpuinfo != NULL) {
-      char line[1000];
-      int num_cpus = 0;
-      std::string cpu_type;
-      std::string cache_size;
-      while (fgets(line, sizeof(line), cpuinfo) != NULL) {
-        const char* sep = strchr(line, ':');
-        if (sep == NULL) {
-          continue;
-        }
-        Slice key = TrimSpace(Slice(line, sep - 1 - line));
-        Slice val = TrimSpace(Slice(sep + 1));
-        if (key == "model name") {
-          ++num_cpus;
-          cpu_type = val.ToString();
-        } else if (key == "cache size") {
-          cache_size = val.ToString();
-        }
-      }
-      fclose(cpuinfo);
-      fprintf(stderr, "CPU:        %d * %s\n", num_cpus, cpu_type.c_str());
-      fprintf(stderr, "CPUCache:   %s\n", cache_size.c_str());
-    }
-#endif
-  }
-
- public:
-  Benchmark()
-  : cache_(FLAGS_cache_size >= 0 ? NewLRUCache(FLAGS_cache_size) : NULL),
-    filter_policy_(FLAGS_bloom_bits >= 0
-                   ? NewBloomFilterPolicy(FLAGS_bloom_bits)
-                   : NULL),
-    db_(NULL),
-    num_(FLAGS_num),
-    value_size_(FLAGS_value_size),
-    entries_per_batch_(1),
-    reads_(FLAGS_reads < 0 ? FLAGS_num : FLAGS_reads),
-    heap_counter_(0) {
-    std::vector<std::string> files;
-    Env::Default()->GetChildren(FLAGS_db, &files);
-    for (size_t i = 0; i < files.size(); i++) {
-      if (Slice(files[i]).starts_with("heap-")) {
-        Env::Default()->DeleteFile(std::string(FLAGS_db) + "/" + files[i]);
-      }
-    }
-    if (!FLAGS_use_existing_db) {
-      DestroyDB(FLAGS_db, Options());
-    }
-  }
-
-  ~Benchmark() {
-    delete db_;
-    delete cache_;
-    delete filter_policy_;
-  }
-
-  void Run() {
-    PrintHeader();
-    Open();
-
-    const char* benchmarks = FLAGS_benchmarks;
-    while (benchmarks != NULL) {
-      const char* sep = strchr(benchmarks, ',');
-      Slice name;
-      if (sep == NULL) {
-        name = benchmarks;
-        benchmarks = NULL;
-      } else {
-        name = Slice(benchmarks, sep - benchmarks);
-        benchmarks = sep + 1;
-      }
-
-      // Reset parameters that may be overridden below
-      num_ = FLAGS_num;
-      reads_ = (FLAGS_reads < 0 ? FLAGS_num : FLAGS_reads);
-      value_size_ = FLAGS_value_size;
-      entries_per_batch_ = 1;
-      write_options_ = WriteOptions();
-
-      void (Benchmark::*method)(ThreadState*) = NULL;
-      bool fresh_db = false;
-      int num_threads = FLAGS_threads;
-
-      if (name == Slice("open")) {
-        method = &Benchmark::OpenBench;
-        num_ /= 10000;
-        if (num_ < 1) num_ = 1;
-      } else if (name == Slice("fillseq")) {
-        fresh_db = true;
-        method = &Benchmark::WriteSeq;
-      } else if (name == Slice("fillbatch")) {
-        fresh_db = true;
-        entries_per_batch_ = 1000;
-        method = &Benchmark::WriteSeq;
-      } else if (name == Slice("fillrandom")) {
-        fresh_db = true;
-        method = &Benchmark::WriteRandom;
-      } else if (name == Slice("overwrite")) {
-        fresh_db = false;
-        method = &Benchmark::WriteRandom;
-      } else if (name == Slice("fillsync")) {
-        fresh_db = true;
-        num_ /= 1000;
-        write_options_.sync = true;
-        method = &Benchmark::WriteRandom;
-      } else if (name == Slice("fill100K")) {
-        fresh_db = true;
-        num_ /= 1000;
-        value_size_ = 100 * 1000;
-        method = &Benchmark::WriteRandom;
-      } else if (name == Slice("readseq")) {
-        method = &Benchmark::ReadSequential;
-      } else if (name == Slice("readreverse")) {
-        method = &Benchmark::ReadReverse;
-      } else if (name == Slice("readrandom")) {
-        method = &Benchmark::ReadRandom;
-      } else if (name == Slice("readmissing")) {
-        method = &Benchmark::ReadMissing;
-      } else if (name == Slice("seekrandom")) {
-        method = &Benchmark::SeekRandom;
-      } else if (name == Slice("readhot")) {
-        method = &Benchmark::ReadHot;
-      } else if (name == Slice("readrandomsmall")) {
-        reads_ /= 1000;
-        method = &Benchmark::ReadRandom;
-      } else if (name == Slice("deleteseq")) {
-        method = &Benchmark::DeleteSeq;
-      } else if (name == Slice("deleterandom")) {
-        method = &Benchmark::DeleteRandom;
-      } else if (name == Slice("readwhilewriting")) {
-        num_threads++;  // Add extra thread for writing
-        method = &Benchmark::ReadWhileWriting;
-      } else if (name == Slice("compact")) {
-        method = &Benchmark::Compact;
-      } else if (name == Slice("crc32c")) {
-        method = &Benchmark::Crc32c;
-      } else if (name == Slice("acquireload")) {
-        method = &Benchmark::AcquireLoad;
-      } else if (name == Slice("snappycomp")) {
-        method = &Benchmark::SnappyCompress;
-      } else if (name == Slice("snappyuncomp")) {
-        method = &Benchmark::SnappyUncompress;
-      } else if (name == Slice("heapprofile")) {
-        HeapProfile();
-      } else if (name == Slice("stats")) {
-        PrintStats("leveldb.stats");
-      } else if (name == Slice("sstables")) {
-        PrintStats("leveldb.sstables");
-      } else {
-        if (name != Slice()) {  // No error message for empty name
-          fprintf(stderr, "unknown benchmark '%s'\n", name.ToString().c_str());
-        }
-      }
-
-      if (fresh_db) {
-        if (FLAGS_use_existing_db) {
-          fprintf(stdout, "%-12s : skipped (--use_existing_db is true)\n",
-                  name.ToString().c_str());
-          method = NULL;
-        } else {
-          delete db_;
-          db_ = NULL;
-          DestroyDB(FLAGS_db, Options());
-          Open();
-        }
-      }
-
-      if (method != NULL) {
-        RunBenchmark(num_threads, name, method);
-      }
-    }
-  }
-
- private:
-  struct ThreadArg {
-    Benchmark* bm;
-    SharedState* shared;
-    ThreadState* thread;
-    void (Benchmark::*method)(ThreadState*);
-  };
-
-  static void ThreadBody(void* v) {
-    ThreadArg* arg = reinterpret_cast<ThreadArg*>(v);
-    SharedState* shared = arg->shared;
-    ThreadState* thread = arg->thread;
-    {
-      MutexLock l(&shared->mu);
-      shared->num_initialized++;
-      if (shared->num_initialized >= shared->total) {
-        shared->cv.SignalAll();
-      }
-      while (!shared->start) {
-        shared->cv.Wait();
-      }
-    }
-
-    thread->stats.Start();
-    (arg->bm->*(arg->method))(thread);
-    thread->stats.Stop();
-
-    {
-      MutexLock l(&shared->mu);
-      shared->num_done++;
-      if (shared->num_done >= shared->total) {
-        shared->cv.SignalAll();
-      }
-    }
-  }
-
-  void RunBenchmark(int n, Slice name,
-                    void (Benchmark::*method)(ThreadState*)) {
-    SharedState shared;
-    shared.total = n;
-    shared.num_initialized = 0;
-    shared.num_done = 0;
-    shared.start = false;
-
-    ThreadArg* arg = new ThreadArg[n];
-    for (int i = 0; i < n; i++) {
-      arg[i].bm = this;
-      arg[i].method = method;
-      arg[i].shared = &shared;
-      arg[i].thread = new ThreadState(i);
-      arg[i].thread->shared = &shared;
-      Env::Default()->StartThread(ThreadBody, &arg[i]);
-    }
-
-    shared.mu.Lock();
-    while (shared.num_initialized < n) {
-      shared.cv.Wait();
-    }
-
-    shared.start = true;
-    shared.cv.SignalAll();
-    while (shared.num_done < n) {
-      shared.cv.Wait();
-    }
-    shared.mu.Unlock();
-
-    for (int i = 1; i < n; i++) {
-      arg[0].thread->stats.Merge(arg[i].thread->stats);
-    }
-    arg[0].thread->stats.Report(name);
-
-    for (int i = 0; i < n; i++) {
-      delete arg[i].thread;
-    }
-    delete[] arg;
-  }
-
-  void Crc32c(ThreadState* thread) {
-    // Checksum about 500MB of data total
-    const int size = 4096;
-    const char* label = "(4K per op)";
-    std::string data(size, 'x');
-    int64_t bytes = 0;
-    uint32_t crc = 0;
-    while (bytes < 500 * 1048576) {
-      crc = crc32c::Value(data.data(), size);
-      thread->stats.FinishedSingleOp();
-      bytes += size;
-    }
-    // Print so result is not dead
-    fprintf(stderr, "... crc=0x%x\r", static_cast<unsigned int>(crc));
-
-    thread->stats.AddBytes(bytes);
-    thread->stats.AddMessage(label);
-  }
-
-  void AcquireLoad(ThreadState* thread) {
-    int dummy;
-    port::AtomicPointer ap(&dummy);
-    int count = 0;
-    void *ptr = NULL;
-    thread->stats.AddMessage("(each op is 1000 loads)");
-    while (count < 100000) {
-      for (int i = 0; i < 1000; i++) {
-        ptr = ap.Acquire_Load();
-      }
-      count++;
-      thread->stats.FinishedSingleOp();
-    }
-    if (ptr == NULL) exit(1); // Disable unused variable warning.
-  }
-
-  void SnappyCompress(ThreadState* thread) {
-    RandomGenerator gen;
-    Slice input = gen.Generate(Options().block_size);
-    int64_t bytes = 0;
-    int64_t produced = 0;
-    bool ok = true;
-    std::string compressed;
-    while (ok && bytes < 1024 * 1048576) {  // Compress 1G
-      ok = port::Snappy_Compress(input.data(), input.size(), &compressed);
-      produced += compressed.size();
-      bytes += input.size();
-      thread->stats.FinishedSingleOp();
-    }
-
-    if (!ok) {
-      thread->stats.AddMessage("(snappy failure)");
-    } else {
-      char buf[100];
-      snprintf(buf, sizeof(buf), "(output: %.1f%%)",
-               (produced * 100.0) / bytes);
-      thread->stats.AddMessage(buf);
-      thread->stats.AddBytes(bytes);
-    }
-  }
-
-  void SnappyUncompress(ThreadState* thread) {
-    RandomGenerator gen;
-    Slice input = gen.Generate(Options().block_size);
-    std::string compressed;
-    bool ok = port::Snappy_Compress(input.data(), input.size(), &compressed);
-    int64_t bytes = 0;
-    char* uncompressed = new char[input.size()];
-    while (ok && bytes < 1024 * 1048576) {  // Compress 1G
-      ok =  port::Snappy_Uncompress(compressed.data(), compressed.size(),
-                                    uncompressed);
-      bytes += input.size();
-      thread->stats.FinishedSingleOp();
-    }
-    delete[] uncompressed;
-
-    if (!ok) {
-      thread->stats.AddMessage("(snappy failure)");
-    } else {
-      thread->stats.AddBytes(bytes);
-    }
-  }
-
-  void Open() {
-    assert(db_ == NULL);
-    Options options;
-    options.create_if_missing = !FLAGS_use_existing_db;
-    options.block_cache = cache_;
-    options.write_buffer_size = FLAGS_write_buffer_size;
-    options.max_open_files = FLAGS_open_files;
-    options.filter_policy = filter_policy_;
-    Status s = DB::Open(options, FLAGS_db, &db_);
-    if (!s.ok()) {
-      fprintf(stderr, "open error: %s\n", s.ToString().c_str());
-      exit(1);
-    }
-  }
-
-  void OpenBench(ThreadState* thread) {
-    for (int i = 0; i < num_; i++) {
-      delete db_;
-      Open();
-      thread->stats.FinishedSingleOp();
-    }
-  }
-
-  void WriteSeq(ThreadState* thread) {
-    DoWrite(thread, true);
-  }
-
-  void WriteRandom(ThreadState* thread) {
-    DoWrite(thread, false);
-  }
-
-  void DoWrite(ThreadState* thread, bool seq) {
-    if (num_ != FLAGS_num) {
-      char msg[100];
-      snprintf(msg, sizeof(msg), "(%d ops)", num_);
-      thread->stats.AddMessage(msg);
-    }
-
-    RandomGenerator gen;
-    WriteBatch batch;
-    Status s;
-    int64_t bytes = 0;
-    for (int i = 0; i < num_; i += entries_per_batch_) {
-      batch.Clear();
-      for (int j = 0; j < entries_per_batch_; j++) {
-        const int k = seq ? i+j : (thread->rand.Next() % FLAGS_num);
-        char key[100];
-        snprintf(key, sizeof(key), "%016d", k);
-        batch.Put(key, gen.Generate(value_size_));
-        bytes += value_size_ + strlen(key);
-        thread->stats.FinishedSingleOp();
-      }
-      s = db_->Write(write_options_, &batch);
-      if (!s.ok()) {
-        fprintf(stderr, "put error: %s\n", s.ToString().c_str());
-        exit(1);
-      }
-    }
-    thread->stats.AddBytes(bytes);
-  }
-
-  void ReadSequential(ThreadState* thread) {
-    Iterator* iter = db_->NewIterator(ReadOptions());
-    int i = 0;
-    int64_t bytes = 0;
-    for (iter->SeekToFirst(); i < reads_ && iter->Valid(); iter->Next()) {
-      bytes += iter->key().size() + iter->value().size();
-      thread->stats.FinishedSingleOp();
-      ++i;
-    }
-    delete iter;
-    thread->stats.AddBytes(bytes);
-  }
-
-  void ReadReverse(ThreadState* thread) {
-    Iterator* iter = db_->NewIterator(ReadOptions());
-    int i = 0;
-    int64_t bytes = 0;
-    for (iter->SeekToLast(); i < reads_ && iter->Valid(); iter->Prev()) {
-      bytes += iter->key().size() + iter->value().size();
-      thread->stats.FinishedSingleOp();
-      ++i;
-    }
-    delete iter;
-    thread->stats.AddBytes(bytes);
-  }
-
-  void ReadRandom(ThreadState* thread) {
-    ReadOptions options;
-    std::string value;
-    int found = 0;
-    for (int i = 0; i < reads_; i++) {
-      char key[100];
-      const int k = thread->rand.Next() % FLAGS_num;
-      snprintf(key, sizeof(key), "%016d", k);
-      if (db_->Get(options, key, &value).ok()) {
-        found++;
-      }
-      thread->stats.FinishedSingleOp();
-    }
-    char msg[100];
-    snprintf(msg, sizeof(msg), "(%d of %d found)", found, num_);
-    thread->stats.AddMessage(msg);
-  }
-
-  void ReadMissing(ThreadState* thread) {
-    ReadOptions options;
-    std::string value;
-    for (int i = 0; i < reads_; i++) {
-      char key[100];
-      const int k = thread->rand.Next() % FLAGS_num;
-      snprintf(key, sizeof(key), "%016d.", k);
-      db_->Get(options, key, &value);
-      thread->stats.FinishedSingleOp();
-    }
-  }
-
-  void ReadHot(ThreadState* thread) {
-    ReadOptions options;
-    std::string value;
-    const int range = (FLAGS_num + 99) / 100;
-    for (int i = 0; i < reads_; i++) {
-      char key[100];
-      const int k = thread->rand.Next() % range;
-      snprintf(key, sizeof(key), "%016d", k);
-      db_->Get(options, key, &value);
-      thread->stats.FinishedSingleOp();
-    }
-  }
-
-  void SeekRandom(ThreadState* thread) {
-    ReadOptions options;
-    int found = 0;
-    for (int i = 0; i < reads_; i++) {
-      Iterator* iter = db_->NewIterator(options);
-      char key[100];
-      const int k = thread->rand.Next() % FLAGS_num;
-      snprintf(key, sizeof(key), "%016d", k);
-      iter->Seek(key);
-      if (iter->Valid() && iter->key() == key) found++;
-      delete iter;
-      thread->stats.FinishedSingleOp();
-    }
-    char msg[100];
-    snprintf(msg, sizeof(msg), "(%d of %d found)", found, num_);
-    thread->stats.AddMessage(msg);
-  }
-
-  void DoDelete(ThreadState* thread, bool seq) {
-    RandomGenerator gen;
-    WriteBatch batch;
-    Status s;
-    for (int i = 0; i < num_; i += entries_per_batch_) {
-      batch.Clear();
-      for (int j = 0; j < entries_per_batch_; j++) {
-        const int k = seq ? i+j : (thread->rand.Next() % FLAGS_num);
-        char key[100];
-        snprintf(key, sizeof(key), "%016d", k);
-        batch.Delete(key);
-        thread->stats.FinishedSingleOp();
-      }
-      s = db_->Write(write_options_, &batch);
-      if (!s.ok()) {
-        fprintf(stderr, "del error: %s\n", s.ToString().c_str());
-        exit(1);
-      }
-    }
-  }
-
-  void DeleteSeq(ThreadState* thread) {
-    DoDelete(thread, true);
-  }
-
-  void DeleteRandom(ThreadState* thread) {
-    DoDelete(thread, false);
-  }
-
-  void ReadWhileWriting(ThreadState* thread) {
-    if (thread->tid > 0) {
-      ReadRandom(thread);
-    } else {
-      // Special thread that keeps writing until other threads are done.
-      RandomGenerator gen;
-      while (true) {
-        {
-          MutexLock l(&thread->shared->mu);
-          if (thread->shared->num_done + 1 >= thread->shared->num_initialized) {
-            // Other threads have finished
-            break;
-          }
-        }
-
-        const int k = thread->rand.Next() % FLAGS_num;
-        char key[100];
-        snprintf(key, sizeof(key), "%016d", k);
-        Status s = db_->Put(write_options_, key, gen.Generate(value_size_));
-        if (!s.ok()) {
-          fprintf(stderr, "put error: %s\n", s.ToString().c_str());
-          exit(1);
-        }
-      }
-
-      // Do not count any of the preceding work/delay in stats.
-      thread->stats.Start();
-    }
-  }
-
-  void Compact(ThreadState* thread) {
-    db_->CompactRange(NULL, NULL);
-  }
-
-  void PrintStats(const char* key) {
-    std::string stats;
-    if (!db_->GetProperty(key, &stats)) {
-      stats = "(failed)";
-    }
-    fprintf(stdout, "\n%s\n", stats.c_str());
-  }
-
-  static void WriteToFile(void* arg, const char* buf, int n) {
-    reinterpret_cast<WritableFile*>(arg)->Append(Slice(buf, n));
-  }
-
-  void HeapProfile() {
-    char fname[100];
-    snprintf(fname, sizeof(fname), "%s/heap-%04d", FLAGS_db, ++heap_counter_);
-    WritableFile* file;
-    Status s = Env::Default()->NewWritableFile(fname, &file);
-    if (!s.ok()) {
-      fprintf(stderr, "%s\n", s.ToString().c_str());
-      return;
-    }
-    bool ok = port::GetHeapProfile(WriteToFile, file);
-    delete file;
-    if (!ok) {
-      fprintf(stderr, "heap profiling not supported\n");
-      Env::Default()->DeleteFile(fname);
-    }
-  }
-};
-
-}  // namespace leveldb
-
-int main(int argc, char** argv) {
-  FLAGS_write_buffer_size = leveldb::Options().write_buffer_size;
-  FLAGS_open_files = leveldb::Options().max_open_files;
-  std::string default_db_path;
-
-  for (int i = 1; i < argc; i++) {
-    double d;
-    int n;
-    char junk;
-    if (leveldb::Slice(argv[i]).starts_with("--benchmarks=")) {
-      FLAGS_benchmarks = argv[i] + strlen("--benchmarks=");
-    } else if (sscanf(argv[i], "--compression_ratio=%lf%c", &d, &junk) == 1) {
-      FLAGS_compression_ratio = d;
-    } else if (sscanf(argv[i], "--histogram=%d%c", &n, &junk) == 1 &&
-               (n == 0 || n == 1)) {
-      FLAGS_histogram = n;
-    } else if (sscanf(argv[i], "--use_existing_db=%d%c", &n, &junk) == 1 &&
-               (n == 0 || n == 1)) {
-      FLAGS_use_existing_db = n;
-    } else if (sscanf(argv[i], "--num=%d%c", &n, &junk) == 1) {
-      FLAGS_num = n;
-    } else if (sscanf(argv[i], "--reads=%d%c", &n, &junk) == 1) {
-      FLAGS_reads = n;
-    } else if (sscanf(argv[i], "--threads=%d%c", &n, &junk) == 1) {
-      FLAGS_threads = n;
-    } else if (sscanf(argv[i], "--value_size=%d%c", &n, &junk) == 1) {
-      FLAGS_value_size = n;
-    } else if (sscanf(argv[i], "--write_buffer_size=%d%c", &n, &junk) == 1) {
-      FLAGS_write_buffer_size = n;
-    } else if (sscanf(argv[i], "--cache_size=%d%c", &n, &junk) == 1) {
-      FLAGS_cache_size = n;
-    } else if (sscanf(argv[i], "--bloom_bits=%d%c", &n, &junk) == 1) {
-      FLAGS_bloom_bits = n;
-    } else if (sscanf(argv[i], "--open_files=%d%c", &n, &junk) == 1) {
-      FLAGS_open_files = n;
-    } else if (strncmp(argv[i], "--db=", 5) == 0) {
-      FLAGS_db = argv[i] + 5;
-    } else {
-      fprintf(stderr, "Invalid flag '%s'\n", argv[i]);
-      exit(1);
-    }
-  }
-
-  // Choose a location for the test database if none given with --db=<path>
-  if (FLAGS_db == NULL) {
-      leveldb::Env::Default()->GetTestDirectory(&default_db_path);
-      default_db_path += "/dbbench";
-      FLAGS_db = default_db_path.c_str();
-  }
-
-  leveldb::Benchmark benchmark;
-  benchmark.Run();
-  return 0;
-}
diff --git a/db/db_impl.cc b/db/db_impl.cc
index cc1cea4..6e8fe61 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -4,12 +4,15 @@
 
 #include "db/db_impl.h"
 
+#include <stdint.h>
+#include <stdio.h>
+
 #include <algorithm>
+#include <atomic>
 #include <set>
 #include <string>
-#include <stdint.h>
-#include <stdio.h>
 #include <vector>
+
 #include "db/builder.h"
 #include "db/db_iter.h"
 #include "db/dbformat.h"
@@ -39,16 +42,33 @@ const int kNumNonTableCacheFiles = 10;
 
 // Information kept for every waiting writer
 struct DBImpl::Writer {
+  explicit Writer(port::Mutex* mu)
+      : batch(nullptr), sync(false), done(false), cv(mu) {}
+
   Status status;
   WriteBatch* batch;
   bool sync;
   bool done;
   port::CondVar cv;
-
-  explicit Writer(port::Mutex* mu) : cv(mu) { }
 };
 
 struct DBImpl::CompactionState {
+  // Files produced by compaction
+  struct Output {
+    uint64_t number;
+    uint64_t file_size;
+    InternalKey smallest, largest;
+  };
+
+  Output* current_output() { return &outputs[outputs.size() - 1]; }
+
+  explicit CompactionState(Compaction* c)
+      : compaction(c),
+        smallest_snapshot(0),
+        outfile(nullptr),
+        builder(nullptr),
+        total_bytes(0) {}
+
   Compaction* const compaction;
 
   // Sequence numbers < smallest_snapshot are not significant since we
@@ -57,12 +77,6 @@ struct DBImpl::CompactionState {
   // we can drop all entries for the same key with sequence numbers < S.
   SequenceNumber smallest_snapshot;
 
-  // Files produced by compaction
-  struct Output {
-    uint64_t number;
-    uint64_t file_size;
-    InternalKey smallest, largest;
-  };
   std::vector<Output> outputs;
 
   // State kept for output being generated
@@ -70,19 +84,10 @@ struct DBImpl::CompactionState {
   TableBuilder* builder;
 
   uint64_t total_bytes;
-
-  Output* current_output() { return &outputs[outputs.size()-1]; }
-
-  explicit CompactionState(Compaction* c)
-      : compaction(c),
-        outfile(NULL),
-        builder(NULL),
-        total_bytes(0) {
-  }
 };
 
 // Fix user-supplied options to be reasonable
-template <class T,class V>
+template <class T, class V>
 static void ClipToRange(T* ptr, V minvalue, V maxvalue) {
   if (static_cast<V>(*ptr) > maxvalue) *ptr = maxvalue;
   if (static_cast<V>(*ptr) < minvalue) *ptr = minvalue;
@@ -93,26 +98,32 @@ Options SanitizeOptions(const std::string& dbname,
                         const Options& src) {
   Options result = src;
   result.comparator = icmp;
-  result.filter_policy = (src.filter_policy != NULL) ? ipolicy : NULL;
-  ClipToRange(&result.max_open_files,    64 + kNumNonTableCacheFiles, 50000);
-  ClipToRange(&result.write_buffer_size, 64<<10,                      1<<30);
-  ClipToRange(&result.block_size,        1<<10,                       4<<20);
-  if (result.info_log == NULL) {
+  result.filter_policy = (src.filter_policy != nullptr) ? ipolicy : nullptr;
+  ClipToRange(&result.max_open_files, 64 + kNumNonTableCacheFiles, 50000);
+  ClipToRange(&result.write_buffer_size, 64 << 10, 1 << 30);
+  ClipToRange(&result.max_file_size, 1 << 20, 1 << 30);
+  ClipToRange(&result.block_size, 1 << 10, 4 << 20);
+  if (result.info_log == nullptr) {
     // Open a log file in the same directory as the db
     src.env->CreateDir(dbname);  // In case it does not exist
     src.env->RenameFile(InfoLogFileName(dbname), OldInfoLogFileName(dbname));
     Status s = src.env->NewLogger(InfoLogFileName(dbname), &result.info_log);
     if (!s.ok()) {
       // No place suitable for logging
-      result.info_log = NULL;
+      result.info_log = nullptr;
     }
   }
-  if (result.block_cache == NULL) {
+  if (result.block_cache == nullptr) {
     result.block_cache = NewLRUCache(8 << 20);
   }
   return result;
 }
 
+static int TableCacheSize(const Options& sanitized_options) {
+  // Reserve ten files or so for other uses and give the rest to TableCache.
+  return sanitized_options.max_open_files - kNumNonTableCacheFiles;
+}
+
 DBImpl::DBImpl(const Options& raw_options, const std::string& dbname)
     : env_(raw_options.env),
       internal_comparator_(raw_options.comparator),
@@ -122,45 +133,39 @@ DBImpl::DBImpl(const Options& raw_options, const std::string& dbname)
       owns_info_log_(options_.info_log != raw_options.info_log),
       owns_cache_(options_.block_cache != raw_options.block_cache),
       dbname_(dbname),
-      db_lock_(NULL),
-      shutting_down_(NULL),
-      bg_cv_(&mutex_),
-      mem_(new MemTable(internal_comparator_)),
-      imm_(NULL),
-      logfile_(NULL),
+      table_cache_(new TableCache(dbname_, options_, TableCacheSize(options_))),
+      db_lock_(nullptr),
+      shutting_down_(false),
+      background_work_finished_signal_(&mutex_),
+      mem_(nullptr),
+      imm_(nullptr),
+      has_imm_(false),
+      logfile_(nullptr),
       logfile_number_(0),
-      log_(NULL),
+      log_(nullptr),
       seed_(0),
       tmp_batch_(new WriteBatch),
-      bg_compaction_scheduled_(false),
-      manual_compaction_(NULL) {
-  mem_->Ref();
-  has_imm_.Release_Store(NULL);
-
-  // Reserve ten files or so for other uses and give the rest to TableCache.
-  const int table_cache_size = options_.max_open_files - kNumNonTableCacheFiles;
-  table_cache_ = new TableCache(dbname_, &options_, table_cache_size);
-
-  versions_ = new VersionSet(dbname_, &options_, table_cache_,
-                             &internal_comparator_);
-}
+      background_compaction_scheduled_(false),
+      manual_compaction_(nullptr),
+      versions_(new VersionSet(dbname_, &options_, table_cache_,
+                               &internal_comparator_)) {}
 
 DBImpl::~DBImpl() {
-  // Wait for background work to finish
+  // Wait for background work to finish.
   mutex_.Lock();
-  shutting_down_.Release_Store(this);  // Any non-NULL value is ok
-  while (bg_compaction_scheduled_) {
-    bg_cv_.Wait();
+  shutting_down_.store(true, std::memory_order_release);
+  while (background_compaction_scheduled_) {
+    background_work_finished_signal_.Wait();
   }
   mutex_.Unlock();
 
-  if (db_lock_ != NULL) {
+  if (db_lock_ != nullptr) {
     env_->UnlockFile(db_lock_);
   }
 
   delete versions_;
-  if (mem_ != NULL) mem_->Unref();
-  if (imm_ != NULL) imm_->Unref();
+  if (mem_ != nullptr) mem_->Unref();
+  if (imm_ != nullptr) imm_->Unref();
   delete tmp_batch_;
   delete log_;
   delete logfile_;
@@ -237,7 +242,6 @@ void DBImpl::DeleteObsoleteFiles() {
 
   // Unlock while deleting obsolete files
   mutex_.Unlock();
-
   uint64_t number;
   FileType type;
   for (size_t i = 0; i < filenames.size(); i++) {
@@ -272,8 +276,7 @@ void DBImpl::DeleteObsoleteFiles() {
         if (type == kTableFile) {
           table_cache_->Evict(number);
         }
-        Log(options_.info_log, "Delete type=%d #%lld\n",
-            int(type),
+        Log(options_.info_log, "Delete type=%d #%lld\n", static_cast<int>(type),
             static_cast<unsigned long long>(number));
         env_->DeleteFile(dbname_ + "/" + filenames[i]);
       }
@@ -282,14 +285,14 @@ void DBImpl::DeleteObsoleteFiles() {
   mutex_.Lock();
 }
 
-Status DBImpl::Recover(VersionEdit* edit) {
+Status DBImpl::Recover(VersionEdit* edit, bool* save_manifest) {
   mutex_.AssertHeld();
 
   // Ignore error from CreateDir since the creation of the DB is
   // committed only when the descriptor is created, and this directory
   // may already exist from a previous failed creation attempt.
   env_->CreateDir(dbname_);
-  assert(db_lock_ == NULL);
+  assert(db_lock_ == nullptr);
   Status s = env_->LockFile(LockFileName(dbname_), &db_lock_);
   if (!s.ok()) {
     return s;
@@ -307,82 +310,85 @@ Status DBImpl::Recover(VersionEdit* edit) {
     }
   } else {
     if (options_.error_if_exists) {
-      return Status::InvalidArgument(
-          dbname_, "exists (error_if_exists is true)");
+      return Status::InvalidArgument(dbname_,
+                                     "exists (error_if_exists is true)");
     }
   }
 
-  s = versions_->Recover();
-  if (s.ok()) {
-    SequenceNumber max_sequence(0);
-
-    // Recover from all newer log files than the ones named in the
-    // descriptor (new log files may have been added by the previous
-    // incarnation without registering them in the descriptor).
-    //
-    // Note that PrevLogNumber() is no longer used, but we pay
-    // attention to it in case we are recovering a database
-    // produced by an older version of leveldb.
-    const uint64_t min_log = versions_->LogNumber();
-    const uint64_t prev_log = versions_->PrevLogNumber();
-    std::vector<std::string> filenames;
-    s = env_->GetChildren(dbname_, &filenames);
+  s = versions_->Recover(save_manifest);
+  if (!s.ok()) {
+    return s;
+  }
+  SequenceNumber max_sequence(0);
+
+  // Recover from all newer log files than the ones named in the
+  // descriptor (new log files may have been added by the previous
+  // incarnation without registering them in the descriptor).
+  //
+  // Note that PrevLogNumber() is no longer used, but we pay
+  // attention to it in case we are recovering a database
+  // produced by an older version of leveldb.
+  const uint64_t min_log = versions_->LogNumber();
+  const uint64_t prev_log = versions_->PrevLogNumber();
+  std::vector<std::string> filenames;
+  s = env_->GetChildren(dbname_, &filenames);
+  if (!s.ok()) {
+    return s;
+  }
+  std::set<uint64_t> expected;
+  versions_->AddLiveFiles(&expected);
+  uint64_t number;
+  FileType type;
+  std::vector<uint64_t> logs;
+  for (size_t i = 0; i < filenames.size(); i++) {
+    if (ParseFileName(filenames[i], &number, &type)) {
+      expected.erase(number);
+      if (type == kLogFile && ((number >= min_log) || (number == prev_log)))
+        logs.push_back(number);
+    }
+  }
+  if (!expected.empty()) {
+    char buf[50];
+    snprintf(buf, sizeof(buf), "%d missing files; e.g.",
+             static_cast<int>(expected.size()));
+    return Status::Corruption(buf, TableFileName(dbname_, *(expected.begin())));
+  }
+
+  // Recover in the order in which the logs were generated
+  std::sort(logs.begin(), logs.end());
+  for (size_t i = 0; i < logs.size(); i++) {
+    s = RecoverLogFile(logs[i], (i == logs.size() - 1), save_manifest, edit,
+                       &max_sequence);
     if (!s.ok()) {
       return s;
     }
-    std::set<uint64_t> expected;
-    versions_->AddLiveFiles(&expected);
-    uint64_t number;
-    FileType type;
-    std::vector<uint64_t> logs;
-    for (size_t i = 0; i < filenames.size(); i++) {
-      if (ParseFileName(filenames[i], &number, &type)) {
-        expected.erase(number);
-        if (type == kLogFile && ((number >= min_log) || (number == prev_log)))
-          logs.push_back(number);
-      }
-    }
-    if (!expected.empty()) {
-      char buf[50];
-      snprintf(buf, sizeof(buf), "%d missing files; e.g.",
-               static_cast<int>(expected.size()));
-      return Status::Corruption(buf, TableFileName(dbname_, *(expected.begin())));
-    }
-
-    // Recover in the order in which the logs were generated
-    std::sort(logs.begin(), logs.end());
-    for (size_t i = 0; i < logs.size(); i++) {
-      s = RecoverLogFile(logs[i], edit, &max_sequence);
 
-      // The previous incarnation may not have written any MANIFEST
-      // records after allocating this log number.  So we manually
-      // update the file number allocation counter in VersionSet.
-      versions_->MarkFileNumberUsed(logs[i]);
-    }
+    // The previous incarnation may not have written any MANIFEST
+    // records after allocating this log number.  So we manually
+    // update the file number allocation counter in VersionSet.
+    versions_->MarkFileNumberUsed(logs[i]);
+  }
 
-    if (s.ok()) {
-      if (versions_->LastSequence() < max_sequence) {
-        versions_->SetLastSequence(max_sequence);
-      }
-    }
+  if (versions_->LastSequence() < max_sequence) {
+    versions_->SetLastSequence(max_sequence);
   }
 
-  return s;
+  return Status::OK();
 }
 
-Status DBImpl::RecoverLogFile(uint64_t log_number,
-                              VersionEdit* edit,
+Status DBImpl::RecoverLogFile(uint64_t log_number, bool last_log,
+                              bool* save_manifest, VersionEdit* edit,
                               SequenceNumber* max_sequence) {
   struct LogReporter : public log::Reader::Reporter {
     Env* env;
     Logger* info_log;
     const char* fname;
-    Status* status;  // NULL if options_.paranoid_checks==false
-    virtual void Corruption(size_t bytes, const Status& s) {
+    Status* status;  // null if options_.paranoid_checks==false
+    void Corruption(size_t bytes, const Status& s) override {
       Log(info_log, "%s%s: dropping %d bytes; %s",
-          (this->status == NULL ? "(ignoring error) " : ""),
-          fname, static_cast<int>(bytes), s.ToString().c_str());
-      if (this->status != NULL && this->status->ok()) *this->status = s;
+          (this->status == nullptr ? "(ignoring error) " : ""), fname,
+          static_cast<int>(bytes), s.ToString().c_str());
+      if (this->status != nullptr && this->status->ok()) *this->status = s;
     }
   };
 
@@ -402,31 +408,30 @@ Status DBImpl::RecoverLogFile(uint64_t log_number,
   reporter.env = env_;
   reporter.info_log = options_.info_log;
   reporter.fname = fname.c_str();
-  reporter.status = (options_.paranoid_checks ? &status : NULL);
+  reporter.status = (options_.paranoid_checks ? &status : nullptr);
   // We intentionally make log::Reader do checksumming even if
   // paranoid_checks==false so that corruptions cause entire commits
   // to be skipped instead of propagating bad information (like overly
   // large sequence numbers).
-  log::Reader reader(file, &reporter, true/*checksum*/,
-                     0/*initial_offset*/);
+  log::Reader reader(file, &reporter, true /*checksum*/, 0 /*initial_offset*/);
   Log(options_.info_log, "Recovering log #%llu",
-      (unsigned long long) log_number);
+      (unsigned long long)log_number);
 
   // Read all the records and add to a memtable
   std::string scratch;
   Slice record;
   WriteBatch batch;
-  MemTable* mem = NULL;
-  while (reader.ReadRecord(&record, &scratch) &&
-         status.ok()) {
+  int compactions = 0;
+  MemTable* mem = nullptr;
+  while (reader.ReadRecord(&record, &scratch) && status.ok()) {
     if (record.size() < 12) {
-      reporter.Corruption(
-          record.size(), Status::Corruption("log record too small"));
+      reporter.Corruption(record.size(),
+                          Status::Corruption("log record too small"));
       continue;
     }
     WriteBatchInternal::SetContents(&batch, record);
 
-    if (mem == NULL) {
+    if (mem == nullptr) {
       mem = new MemTable(internal_comparator_);
       mem->Ref();
     }
@@ -435,33 +440,59 @@ Status DBImpl::RecoverLogFile(uint64_t log_number,
     if (!status.ok()) {
       break;
     }
-    const SequenceNumber last_seq =
-        WriteBatchInternal::Sequence(&batch) +
-        WriteBatchInternal::Count(&batch) - 1;
+    const SequenceNumber last_seq = WriteBatchInternal::Sequence(&batch) +
+                                    WriteBatchInternal::Count(&batch) - 1;
     if (last_seq > *max_sequence) {
       *max_sequence = last_seq;
     }
 
     if (mem->ApproximateMemoryUsage() > options_.write_buffer_size) {
-      status = WriteLevel0Table(mem, edit, NULL);
+      compactions++;
+      *save_manifest = true;
+      status = WriteLevel0Table(mem, edit, nullptr);
+      mem->Unref();
+      mem = nullptr;
       if (!status.ok()) {
         // Reflect errors immediately so that conditions like full
         // file-systems cause the DB::Open() to fail.
         break;
       }
-      mem->Unref();
-      mem = NULL;
     }
   }
 
-  if (status.ok() && mem != NULL) {
-    status = WriteLevel0Table(mem, edit, NULL);
-    // Reflect errors immediately so that conditions like full
-    // file-systems cause the DB::Open() to fail.
+  delete file;
+
+  // See if we should keep reusing the last log file.
+  if (status.ok() && options_.reuse_logs && last_log && compactions == 0) {
+    assert(logfile_ == nullptr);
+    assert(log_ == nullptr);
+    assert(mem_ == nullptr);
+    uint64_t lfile_size;
+    if (env_->GetFileSize(fname, &lfile_size).ok() &&
+        env_->NewAppendableFile(fname, &logfile_).ok()) {
+      Log(options_.info_log, "Reusing old log %s \n", fname.c_str());
+      log_ = new log::Writer(logfile_, lfile_size);
+      logfile_number_ = log_number;
+      if (mem != nullptr) {
+        mem_ = mem;
+        mem = nullptr;
+      } else {
+        // mem can be nullptr if lognum exists but was empty.
+        mem_ = new MemTable(internal_comparator_);
+        mem_->Ref();
+      }
+    }
+  }
+
+  if (mem != nullptr) {
+    // mem did not get reused; compact it.
+    if (status.ok()) {
+      *save_manifest = true;
+      status = WriteLevel0Table(mem, edit, nullptr);
+    }
+    mem->Unref();
   }
 
-  if (mem != NULL) mem->Unref();
-  delete file;
   return status;
 }
 
@@ -474,7 +505,7 @@ Status DBImpl::WriteLevel0Table(MemTable* mem, VersionEdit* edit,
   pending_outputs_.insert(meta.number);
   Iterator* iter = mem->NewIterator();
   Log(options_.info_log, "Level-0 table #%llu: started",
-      (unsigned long long) meta.number);
+      (unsigned long long)meta.number);
 
   Status s;
   {
@@ -484,24 +515,22 @@ Status DBImpl::WriteLevel0Table(MemTable* mem, VersionEdit* edit,
   }
 
   Log(options_.info_log, "Level-0 table #%llu: %lld bytes %s",
-      (unsigned long long) meta.number,
-      (unsigned long long) meta.file_size,
+      (unsigned long long)meta.number, (unsigned long long)meta.file_size,
       s.ToString().c_str());
   delete iter;
   pending_outputs_.erase(meta.number);
 
-
   // Note that if file_size is zero, the file has been deleted and
   // should not be added to the manifest.
   int level = 0;
   if (s.ok() && meta.file_size > 0) {
     const Slice min_user_key = meta.smallest.user_key();
     const Slice max_user_key = meta.largest.user_key();
-    if (base != NULL) {
+    if (base != nullptr) {
       level = base->PickLevelForMemTableOutput(min_user_key, max_user_key);
     }
-    edit->AddFile(level, meta.number, meta.file_size,
-                  meta.smallest, meta.largest);
+    edit->AddFile(level, meta.number, meta.file_size, meta.smallest,
+                  meta.largest);
   }
 
   CompactionStats stats;
@@ -513,7 +542,7 @@ Status DBImpl::WriteLevel0Table(MemTable* mem, VersionEdit* edit,
 
 void DBImpl::CompactMemTable() {
   mutex_.AssertHeld();
-  assert(imm_ != NULL);
+  assert(imm_ != nullptr);
 
   // Save the contents of the memtable as a new Table
   VersionEdit edit;
@@ -522,7 +551,7 @@ void DBImpl::CompactMemTable() {
   Status s = WriteLevel0Table(imm_, &edit, base);
   base->Unref();
 
-  if (s.ok() && shutting_down_.Acquire_Load()) {
+  if (s.ok() && shutting_down_.load(std::memory_order_acquire)) {
     s = Status::IOError("Deleting DB during memtable compaction");
   }
 
@@ -536,8 +565,8 @@ void DBImpl::CompactMemTable() {
   if (s.ok()) {
     // Commit to the new state
     imm_->Unref();
-    imm_ = NULL;
-    has_imm_.Release_Store(NULL);
+    imm_ = nullptr;
+    has_imm_.store(false, std::memory_order_release);
     DeleteObsoleteFiles();
   } else {
     RecordBackgroundError(s);
@@ -555,13 +584,14 @@ void DBImpl::CompactRange(const Slice* begin, const Slice* end) {
       }
     }
   }
-  TEST_CompactMemTable(); // TODO(sanjay): Skip if memtable does not overlap
+  TEST_CompactMemTable();  // TODO(sanjay): Skip if memtable does not overlap
   for (int level = 0; level < max_level_with_files; level++) {
     TEST_CompactRange(level, begin, end);
   }
 }
 
-void DBImpl::TEST_CompactRange(int level, const Slice* begin,const Slice* end) {
+void DBImpl::TEST_CompactRange(int level, const Slice* begin,
+                               const Slice* end) {
   assert(level >= 0);
   assert(level + 1 < config::kNumLevels);
 
@@ -570,44 +600,45 @@ void DBImpl::TEST_CompactRange(int level, const Slice* begin,const Slice* end) {
   ManualCompaction manual;
   manual.level = level;
   manual.done = false;
-  if (begin == NULL) {
-    manual.begin = NULL;
+  if (begin == nullptr) {
+    manual.begin = nullptr;
   } else {
     begin_storage = InternalKey(*begin, kMaxSequenceNumber, kValueTypeForSeek);
     manual.begin = &begin_storage;
   }
-  if (end == NULL) {
-    manual.end = NULL;
+  if (end == nullptr) {
+    manual.end = nullptr;
   } else {
     end_storage = InternalKey(*end, 0, static_cast<ValueType>(0));
     manual.end = &end_storage;
   }
 
   MutexLock l(&mutex_);
-  while (!manual.done && !shutting_down_.Acquire_Load() && bg_error_.ok()) {
-    if (manual_compaction_ == NULL) {  // Idle
+  while (!manual.done && !shutting_down_.load(std::memory_order_acquire) &&
+         bg_error_.ok()) {
+    if (manual_compaction_ == nullptr) {  // Idle
       manual_compaction_ = &manual;
       MaybeScheduleCompaction();
     } else {  // Running either my compaction or another compaction.
-      bg_cv_.Wait();
+      background_work_finished_signal_.Wait();
     }
   }
   if (manual_compaction_ == &manual) {
     // Cancel my manual compaction since we aborted early for some reason.
-    manual_compaction_ = NULL;
+    manual_compaction_ = nullptr;
   }
 }
 
 Status DBImpl::TEST_CompactMemTable() {
-  // NULL batch means just wait for earlier writes to be done
-  Status s = Write(WriteOptions(), NULL);
+  // nullptr batch means just wait for earlier writes to be done
+  Status s = Write(WriteOptions(), nullptr);
   if (s.ok()) {
     // Wait until the compaction completes
     MutexLock l(&mutex_);
-    while (imm_ != NULL && bg_error_.ok()) {
-      bg_cv_.Wait();
+    while (imm_ != nullptr && bg_error_.ok()) {
+      background_work_finished_signal_.Wait();
     }
-    if (imm_ != NULL) {
+    if (imm_ != nullptr) {
       s = bg_error_;
     }
   }
@@ -618,24 +649,23 @@ void DBImpl::RecordBackgroundError(const Status& s) {
   mutex_.AssertHeld();
   if (bg_error_.ok()) {
     bg_error_ = s;
-    bg_cv_.SignalAll();
+    background_work_finished_signal_.SignalAll();
   }
 }
 
 void DBImpl::MaybeScheduleCompaction() {
   mutex_.AssertHeld();
-  if (bg_compaction_scheduled_) {
+  if (background_compaction_scheduled_) {
     // Already scheduled
-  } else if (shutting_down_.Acquire_Load()) {
+  } else if (shutting_down_.load(std::memory_order_acquire)) {
     // DB is being deleted; no more background compactions
   } else if (!bg_error_.ok()) {
     // Already got an error; no more changes
-  } else if (imm_ == NULL &&
-             manual_compaction_ == NULL &&
+  } else if (imm_ == nullptr && manual_compaction_ == nullptr &&
              !versions_->NeedsCompaction()) {
     // No work to be done
   } else {
-    bg_compaction_scheduled_ = true;
+    background_compaction_scheduled_ = true;
     env_->Schedule(&DBImpl::BGWork, this);
   }
 }
@@ -646,8 +676,8 @@ void DBImpl::BGWork(void* db) {
 
 void DBImpl::BackgroundCall() {
   MutexLock l(&mutex_);
-  assert(bg_compaction_scheduled_);
-  if (shutting_down_.Acquire_Load()) {
+  assert(background_compaction_scheduled_);
+  if (shutting_down_.load(std::memory_order_acquire)) {
     // No more background work when shutting down.
   } else if (!bg_error_.ok()) {
     // No more background work after a background error.
@@ -655,36 +685,35 @@ void DBImpl::BackgroundCall() {
     BackgroundCompaction();
   }
 
-  bg_compaction_scheduled_ = false;
+  background_compaction_scheduled_ = false;
 
   // Previous compaction may have produced too many files in a level,
   // so reschedule another compaction if needed.
   MaybeScheduleCompaction();
-  bg_cv_.SignalAll();
+  background_work_finished_signal_.SignalAll();
 }
 
 void DBImpl::BackgroundCompaction() {
   mutex_.AssertHeld();
 
-  if (imm_ != NULL) {
+  if (imm_ != nullptr) {
     CompactMemTable();
     return;
   }
 
   Compaction* c;
-  bool is_manual = (manual_compaction_ != NULL);
+  bool is_manual = (manual_compaction_ != nullptr);
   InternalKey manual_end;
   if (is_manual) {
     ManualCompaction* m = manual_compaction_;
     c = versions_->CompactRange(m->level, m->begin, m->end);
-    m->done = (c == NULL);
-    if (c != NULL) {
+    m->done = (c == nullptr);
+    if (c != nullptr) {
       manual_end = c->input(0, c->num_input_files(0) - 1)->largest;
     }
     Log(options_.info_log,
         "Manual compaction at level-%d from %s .. %s; will stop at %s\n",
-        m->level,
-        (m->begin ? m->begin->DebugString().c_str() : "(begin)"),
+        m->level, (m->begin ? m->begin->DebugString().c_str() : "(begin)"),
         (m->end ? m->end->DebugString().c_str() : "(end)"),
         (m->done ? "(end)" : manual_end.DebugString().c_str()));
   } else {
@@ -692,26 +721,24 @@ void DBImpl::BackgroundCompaction() {
   }
 
   Status status;
-  if (c == NULL) {
+  if (c == nullptr) {
     // Nothing to do
   } else if (!is_manual && c->IsTrivialMove()) {
     // Move file to next level
     assert(c->num_input_files(0) == 1);
     FileMetaData* f = c->input(0, 0);
     c->edit()->DeleteFile(c->level(), f->number);
-    c->edit()->AddFile(c->level() + 1, f->number, f->file_size,
-                       f->smallest, f->largest);
+    c->edit()->AddFile(c->level() + 1, f->number, f->file_size, f->smallest,
+                       f->largest);
     status = versions_->LogAndApply(c->edit(), &mutex_);
     if (!status.ok()) {
       RecordBackgroundError(status);
     }
     VersionSet::LevelSummaryStorage tmp;
     Log(options_.info_log, "Moved #%lld to level-%d %lld bytes %s: %s\n",
-        static_cast<unsigned long long>(f->number),
-        c->level() + 1,
+        static_cast<unsigned long long>(f->number), c->level() + 1,
         static_cast<unsigned long long>(f->file_size),
-        status.ToString().c_str(),
-        versions_->LevelSummary(&tmp));
+        status.ToString().c_str(), versions_->LevelSummary(&tmp));
   } else {
     CompactionState* compact = new CompactionState(c);
     status = DoCompactionWork(compact);
@@ -726,11 +753,10 @@ void DBImpl::BackgroundCompaction() {
 
   if (status.ok()) {
     // Done
-  } else if (shutting_down_.Acquire_Load()) {
+  } else if (shutting_down_.load(std::memory_order_acquire)) {
     // Ignore compaction errors found during shutting down
   } else {
-    Log(options_.info_log,
-        "Compaction error: %s", status.ToString().c_str());
+    Log(options_.info_log, "Compaction error: %s", status.ToString().c_str());
   }
 
   if (is_manual) {
@@ -744,18 +770,18 @@ void DBImpl::BackgroundCompaction() {
       m->tmp_storage = manual_end;
       m->begin = &m->tmp_storage;
     }
-    manual_compaction_ = NULL;
+    manual_compaction_ = nullptr;
   }
 }
 
 void DBImpl::CleanupCompaction(CompactionState* compact) {
   mutex_.AssertHeld();
-  if (compact->builder != NULL) {
+  if (compact->builder != nullptr) {
     // May happen if we get a shutdown call in the middle of compaction
     compact->builder->Abandon();
     delete compact->builder;
   } else {
-    assert(compact->outfile == NULL);
+    assert(compact->outfile == nullptr);
   }
   delete compact->outfile;
   for (size_t i = 0; i < compact->outputs.size(); i++) {
@@ -766,8 +792,8 @@ void DBImpl::CleanupCompaction(CompactionState* compact) {
 }
 
 Status DBImpl::OpenCompactionOutputFile(CompactionState* compact) {
-  assert(compact != NULL);
-  assert(compact->builder == NULL);
+  assert(compact != nullptr);
+  assert(compact->builder == nullptr);
   uint64_t file_number;
   {
     mutex_.Lock();
@@ -792,9 +818,9 @@ Status DBImpl::OpenCompactionOutputFile(CompactionState* compact) {
 
 Status DBImpl::FinishCompactionOutputFile(CompactionState* compact,
                                           Iterator* input) {
-  assert(compact != NULL);
-  assert(compact->outfile != NULL);
-  assert(compact->builder != NULL);
+  assert(compact != nullptr);
+  assert(compact->outfile != nullptr);
+  assert(compact->builder != nullptr);
 
   const uint64_t output_number = compact->current_output()->number;
   assert(output_number != 0);
@@ -811,7 +837,7 @@ Status DBImpl::FinishCompactionOutputFile(CompactionState* compact,
   compact->current_output()->file_size = current_bytes;
   compact->total_bytes += current_bytes;
   delete compact->builder;
-  compact->builder = NULL;
+  compact->builder = nullptr;
 
   // Finish and check for file errors
   if (s.ok()) {
@@ -821,34 +847,29 @@ Status DBImpl::FinishCompactionOutputFile(CompactionState* compact,
     s = compact->outfile->Close();
   }
   delete compact->outfile;
-  compact->outfile = NULL;
+  compact->outfile = nullptr;
 
   if (s.ok() && current_entries > 0) {
     // Verify that the table is usable
-    Iterator* iter = table_cache_->NewIterator(ReadOptions(),
-                                               output_number,
-                                               current_bytes);
+    Iterator* iter =
+        table_cache_->NewIterator(ReadOptions(), output_number, current_bytes);
     s = iter->status();
     delete iter;
     if (s.ok()) {
-      Log(options_.info_log,
-          "Generated table #%llu: %lld keys, %lld bytes",
-          (unsigned long long) output_number,
-          (unsigned long long) current_entries,
-          (unsigned long long) current_bytes);
+      Log(options_.info_log, "Generated table #%llu@%d: %lld keys, %lld bytes",
+          (unsigned long long)output_number, compact->compaction->level(),
+          (unsigned long long)current_entries,
+          (unsigned long long)current_bytes);
     }
   }
   return s;
 }
 
-
 Status DBImpl::InstallCompactionResults(CompactionState* compact) {
   mutex_.AssertHeld();
-  Log(options_.info_log,  "Compacted %d@%d + %d@%d files => %lld bytes",
-      compact->compaction->num_input_files(0),
-      compact->compaction->level(),
-      compact->compaction->num_input_files(1),
-      compact->compaction->level() + 1,
+  Log(options_.info_log, "Compacted %d@%d + %d@%d files => %lld bytes",
+      compact->compaction->num_input_files(0), compact->compaction->level(),
+      compact->compaction->num_input_files(1), compact->compaction->level() + 1,
       static_cast<long long>(compact->total_bytes));
 
   // Add compaction outputs
@@ -856,9 +877,8 @@ Status DBImpl::InstallCompactionResults(CompactionState* compact) {
   const int level = compact->compaction->level();
   for (size_t i = 0; i < compact->outputs.size(); i++) {
     const CompactionState::Output& out = compact->outputs[i];
-    compact->compaction->edit()->AddFile(
-        level + 1,
-        out.number, out.file_size, out.smallest, out.largest);
+    compact->compaction->edit()->AddFile(level + 1, out.number, out.file_size,
+                                         out.smallest, out.largest);
   }
   return versions_->LogAndApply(compact->compaction->edit(), &mutex_);
 }
@@ -867,39 +887,40 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
   const uint64_t start_micros = env_->NowMicros();
   int64_t imm_micros = 0;  // Micros spent doing imm_ compactions
 
-  Log(options_.info_log,  "Compacting %d@%d + %d@%d files",
-      compact->compaction->num_input_files(0),
-      compact->compaction->level(),
+  Log(options_.info_log, "Compacting %d@%d + %d@%d files",
+      compact->compaction->num_input_files(0), compact->compaction->level(),
       compact->compaction->num_input_files(1),
       compact->compaction->level() + 1);
 
   assert(versions_->NumLevelFiles(compact->compaction->level()) > 0);
-  assert(compact->builder == NULL);
-  assert(compact->outfile == NULL);
+  assert(compact->builder == nullptr);
+  assert(compact->outfile == nullptr);
   if (snapshots_.empty()) {
     compact->smallest_snapshot = versions_->LastSequence();
   } else {
-    compact->smallest_snapshot = snapshots_.oldest()->number_;
+    compact->smallest_snapshot = snapshots_.oldest()->sequence_number();
   }
 
+  Iterator* input = versions_->MakeInputIterator(compact->compaction);
+
   // Release mutex while we're actually doing the compaction work
   mutex_.Unlock();
 
-  Iterator* input = versions_->MakeInputIterator(compact->compaction);
   input->SeekToFirst();
   Status status;
   ParsedInternalKey ikey;
   std::string current_user_key;
   bool has_current_user_key = false;
   SequenceNumber last_sequence_for_key = kMaxSequenceNumber;
-  for (; input->Valid() && !shutting_down_.Acquire_Load(); ) {
+  while (input->Valid() && !shutting_down_.load(std::memory_order_acquire)) {
     // Prioritize immutable compaction work
-    if (has_imm_.NoBarrier_Load() != NULL) {
+    if (has_imm_.load(std::memory_order_relaxed)) {
       const uint64_t imm_start = env_->NowMicros();
       mutex_.Lock();
-      if (imm_ != NULL) {
+      if (imm_ != nullptr) {
         CompactMemTable();
-        bg_cv_.SignalAll();  // Wakeup MakeRoomForWrite() if necessary
+        // Wake up MakeRoomForWrite() if necessary.
+        background_work_finished_signal_.SignalAll();
       }
       mutex_.Unlock();
       imm_micros += (env_->NowMicros() - imm_start);
@@ -907,7 +928,7 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
 
     Slice key = input->key();
     if (compact->compaction->ShouldStopBefore(key) &&
-        compact->builder != NULL) {
+        compact->builder != nullptr) {
       status = FinishCompactionOutputFile(compact, input);
       if (!status.ok()) {
         break;
@@ -923,8 +944,8 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
       last_sequence_for_key = kMaxSequenceNumber;
     } else {
       if (!has_current_user_key ||
-          user_comparator()->Compare(ikey.user_key,
-                                     Slice(current_user_key)) != 0) {
+          user_comparator()->Compare(ikey.user_key, Slice(current_user_key)) !=
+              0) {
         // First occurrence of this user key
         current_user_key.assign(ikey.user_key.data(), ikey.user_key.size());
         has_current_user_key = true;
@@ -933,7 +954,7 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
 
       if (last_sequence_for_key <= compact->smallest_snapshot) {
         // Hidden by an newer entry for same user key
-        drop = true;    // (A)
+        drop = true;  // (A)
       } else if (ikey.type == kTypeDeletion &&
                  ikey.sequence <= compact->smallest_snapshot &&
                  compact->compaction->IsBaseLevelForKey(ikey.user_key)) {
@@ -961,7 +982,7 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
 
     if (!drop) {
       // Open output file if necessary
-      if (compact->builder == NULL) {
+      if (compact->builder == nullptr) {
         status = OpenCompactionOutputFile(compact);
         if (!status.ok()) {
           break;
@@ -986,17 +1007,17 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
     input->Next();
   }
 
-  if (status.ok() && shutting_down_.Acquire_Load()) {
+  if (status.ok() && shutting_down_.load(std::memory_order_acquire)) {
     status = Status::IOError("Deleting DB during compaction");
   }
-  if (status.ok() && compact->builder != NULL) {
+  if (status.ok() && compact->builder != nullptr) {
     status = FinishCompactionOutputFile(compact, input);
   }
   if (status.ok()) {
     status = input->status();
   }
   delete input;
-  input = NULL;
+  input = nullptr;
 
   CompactionStats stats;
   stats.micros = env_->NowMicros() - start_micros - imm_micros;
@@ -1019,34 +1040,37 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
     RecordBackgroundError(status);
   }
   VersionSet::LevelSummaryStorage tmp;
-  Log(options_.info_log,
-      "compacted to: %s", versions_->LevelSummary(&tmp));
+  Log(options_.info_log, "compacted to: %s", versions_->LevelSummary(&tmp));
   return status;
 }
 
 namespace {
+
 struct IterState {
-  port::Mutex* mu;
-  Version* version;
-  MemTable* mem;
-  MemTable* imm;
+  port::Mutex* const mu;
+  Version* const version GUARDED_BY(mu);
+  MemTable* const mem GUARDED_BY(mu);
+  MemTable* const imm GUARDED_BY(mu);
+
+  IterState(port::Mutex* mutex, MemTable* mem, MemTable* imm, Version* version)
+      : mu(mutex), version(version), mem(mem), imm(imm) {}
 };
 
 static void CleanupIteratorState(void* arg1, void* arg2) {
   IterState* state = reinterpret_cast<IterState*>(arg1);
   state->mu->Lock();
   state->mem->Unref();
-  if (state->imm != NULL) state->imm->Unref();
+  if (state->imm != nullptr) state->imm->Unref();
   state->version->Unref();
   state->mu->Unlock();
   delete state;
 }
-}  // namespace
+
+}  // anonymous namespace
 
 Iterator* DBImpl::NewInternalIterator(const ReadOptions& options,
                                       SequenceNumber* latest_snapshot,
                                       uint32_t* seed) {
-  IterState* cleanup = new IterState;
   mutex_.Lock();
   *latest_snapshot = versions_->LastSequence();
 
@@ -1054,7 +1078,7 @@ Iterator* DBImpl::NewInternalIterator(const ReadOptions& options,
   std::vector<Iterator*> list;
   list.push_back(mem_->NewIterator());
   mem_->Ref();
-  if (imm_ != NULL) {
+  if (imm_ != nullptr) {
     list.push_back(imm_->NewIterator());
     imm_->Ref();
   }
@@ -1063,11 +1087,8 @@ Iterator* DBImpl::NewInternalIterator(const ReadOptions& options,
       NewMergingIterator(&internal_comparator_, &list[0], list.size());
   versions_->current()->Ref();
 
-  cleanup->mu = &mutex_;
-  cleanup->mem = mem_;
-  cleanup->imm = imm_;
-  cleanup->version = versions_->current();
-  internal_iter->RegisterCleanup(CleanupIteratorState, cleanup, NULL);
+  IterState* cleanup = new IterState(&mutex_, mem_, imm_, versions_->current());
+  internal_iter->RegisterCleanup(CleanupIteratorState, cleanup, nullptr);
 
   *seed = ++seed_;
   mutex_.Unlock();
@@ -1085,14 +1106,14 @@ int64_t DBImpl::TEST_MaxNextLevelOverlappingBytes() {
   return versions_->MaxNextLevelOverlappingBytes();
 }
 
-Status DBImpl::Get(const ReadOptions& options,
-                   const Slice& key,
+Status DBImpl::Get(const ReadOptions& options, const Slice& key,
                    std::string* value) {
   Status s;
   MutexLock l(&mutex_);
   SequenceNumber snapshot;
-  if (options.snapshot != NULL) {
-    snapshot = reinterpret_cast<const SnapshotImpl*>(options.snapshot)->number_;
+  if (options.snapshot != nullptr) {
+    snapshot =
+        static_cast<const SnapshotImpl*>(options.snapshot)->sequence_number();
   } else {
     snapshot = versions_->LastSequence();
   }
@@ -1101,7 +1122,7 @@ Status DBImpl::Get(const ReadOptions& options,
   MemTable* imm = imm_;
   Version* current = versions_->current();
   mem->Ref();
-  if (imm != NULL) imm->Ref();
+  if (imm != nullptr) imm->Ref();
   current->Ref();
 
   bool have_stat_update = false;
@@ -1114,7 +1135,7 @@ Status DBImpl::Get(const ReadOptions& options,
     LookupKey lkey(key, snapshot);
     if (mem->Get(lkey, value, &s)) {
       // Done
-    } else if (imm != NULL && imm->Get(lkey, value, &s)) {
+    } else if (imm != nullptr && imm->Get(lkey, value, &s)) {
       // Done
     } else {
       s = current->Get(options, lkey, value, &stats);
@@ -1127,7 +1148,7 @@ Status DBImpl::Get(const ReadOptions& options,
     MaybeScheduleCompaction();
   }
   mem->Unref();
-  if (imm != NULL) imm->Unref();
+  if (imm != nullptr) imm->Unref();
   current->Unref();
   return s;
 }
@@ -1136,12 +1157,12 @@ Iterator* DBImpl::NewIterator(const ReadOptions& options) {
   SequenceNumber latest_snapshot;
   uint32_t seed;
   Iterator* iter = NewInternalIterator(options, &latest_snapshot, &seed);
-  return NewDBIterator(
-      this, user_comparator(), iter,
-      (options.snapshot != NULL
-       ? reinterpret_cast<const SnapshotImpl*>(options.snapshot)->number_
-       : latest_snapshot),
-      seed);
+  return NewDBIterator(this, user_comparator(), iter,
+                       (options.snapshot != nullptr
+                            ? static_cast<const SnapshotImpl*>(options.snapshot)
+                                  ->sequence_number()
+                            : latest_snapshot),
+                       seed);
 }
 
 void DBImpl::RecordReadSample(Slice key) {
@@ -1156,9 +1177,9 @@ const Snapshot* DBImpl::GetSnapshot() {
   return snapshots_.New(versions_->LastSequence());
 }
 
-void DBImpl::ReleaseSnapshot(const Snapshot* s) {
+void DBImpl::ReleaseSnapshot(const Snapshot* snapshot) {
   MutexLock l(&mutex_);
-  snapshots_.Delete(reinterpret_cast<const SnapshotImpl*>(s));
+  snapshots_.Delete(static_cast<const SnapshotImpl*>(snapshot));
 }
 
 // Convenience methods
@@ -1170,9 +1191,9 @@ Status DBImpl::Delete(const WriteOptions& options, const Slice& key) {
   return DB::Delete(options, key);
 }
 
-Status DBImpl::Write(const WriteOptions& options, WriteBatch* my_batch) {
+Status DBImpl::Write(const WriteOptions& options, WriteBatch* updates) {
   Writer w(&mutex_);
-  w.batch = my_batch;
+  w.batch = updates;
   w.sync = options.sync;
   w.done = false;
 
@@ -1186,10 +1207,10 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* my_batch) {
   }
 
   // May temporarily unlock and wait.
-  Status status = MakeRoomForWrite(my_batch == NULL);
+  Status status = MakeRoomForWrite(updates == nullptr);
   uint64_t last_sequence = versions_->LastSequence();
   Writer* last_writer = &w;
-  if (status.ok() && my_batch != NULL) {  // NULL batch is for compactions
+  if (status.ok() && updates != nullptr) {  // nullptr batch is for compactions
     WriteBatch* updates = BuildBatchGroup(&last_writer);
     WriteBatchInternal::SetSequence(updates, last_sequence + 1);
     last_sequence += WriteBatchInternal::Count(updates);
@@ -1244,12 +1265,13 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* my_batch) {
 }
 
 // REQUIRES: Writer list must be non-empty
-// REQUIRES: First writer must have a non-NULL batch
+// REQUIRES: First writer must have a non-null batch
 WriteBatch* DBImpl::BuildBatchGroup(Writer** last_writer) {
+  mutex_.AssertHeld();
   assert(!writers_.empty());
   Writer* first = writers_.front();
   WriteBatch* result = first->batch;
-  assert(result != NULL);
+  assert(result != nullptr);
 
   size_t size = WriteBatchInternal::ByteSize(first->batch);
 
@@ -1257,8 +1279,8 @@ WriteBatch* DBImpl::BuildBatchGroup(Writer** last_writer) {
   // original write is small, limit the growth so we do not slow
   // down the small write too much.
   size_t max_size = 1 << 20;
-  if (size <= (128<<10)) {
-    max_size = size + (128<<10);
+  if (size <= (128 << 10)) {
+    max_size = size + (128 << 10);
   }
 
   *last_writer = first;
@@ -1271,7 +1293,7 @@ WriteBatch* DBImpl::BuildBatchGroup(Writer** last_writer) {
       break;
     }
 
-    if (w->batch != NULL) {
+    if (w->batch != nullptr) {
       size += WriteBatchInternal::ByteSize(w->batch);
       if (size > max_size) {
         // Do not make batch too big
@@ -1304,9 +1326,8 @@ Status DBImpl::MakeRoomForWrite(bool force) {
       // Yield previous error
       s = bg_error_;
       break;
-    } else if (
-        allow_delay &&
-        versions_->NumLevelFiles(0) >= config::kL0_SlowdownWritesTrigger) {
+    } else if (allow_delay && versions_->NumLevelFiles(0) >=
+                                  config::kL0_SlowdownWritesTrigger) {
       // We are getting close to hitting a hard limit on the number of
       // L0 files.  Rather than delaying a single write by several
       // seconds when we hit the hard limit, start delaying each
@@ -1321,20 +1342,20 @@ Status DBImpl::MakeRoomForWrite(bool force) {
                (mem_->ApproximateMemoryUsage() <= options_.write_buffer_size)) {
       // There is room in current memtable
       break;
-    } else if (imm_ != NULL) {
+    } else if (imm_ != nullptr) {
       // We have filled up the current memtable, but the previous
       // one is still being compacted, so we wait.
       Log(options_.info_log, "Current memtable full; waiting...\n");
-      bg_cv_.Wait();
+      background_work_finished_signal_.Wait();
     } else if (versions_->NumLevelFiles(0) >= config::kL0_StopWritesTrigger) {
       // There are too many level-0 files.
       Log(options_.info_log, "Too many L0 files; waiting...\n");
-      bg_cv_.Wait();
+      background_work_finished_signal_.Wait();
     } else {
       // Attempt to switch to a new memtable and trigger compaction of old
       assert(versions_->PrevLogNumber() == 0);
       uint64_t new_log_number = versions_->NewFileNumber();
-      WritableFile* lfile = NULL;
+      WritableFile* lfile = nullptr;
       s = env_->NewWritableFile(LogFileName(dbname_, new_log_number), &lfile);
       if (!s.ok()) {
         // Avoid chewing through file number space in a tight loop.
@@ -1347,10 +1368,10 @@ Status DBImpl::MakeRoomForWrite(bool force) {
       logfile_number_ = new_log_number;
       log_ = new log::Writer(lfile);
       imm_ = mem_;
-      has_imm_.Release_Store(imm_);
+      has_imm_.store(true, std::memory_order_release);
       mem_ = new MemTable(internal_comparator_);
       mem_->Ref();
-      force = false;   // Do not force another compaction if have room
+      force = false;  // Do not force another compaction if have room
       MaybeScheduleCompaction();
     }
   }
@@ -1384,21 +1405,16 @@ bool DBImpl::GetProperty(const Slice& property, std::string* value) {
     snprintf(buf, sizeof(buf),
              "                               Compactions\n"
              "Level  Files Size(MB) Time(sec) Read(MB) Write(MB)\n"
-             "--------------------------------------------------\n"
-             );
+             "--------------------------------------------------\n");
     value->append(buf);
     for (int level = 0; level < config::kNumLevels; level++) {
       int files = versions_->NumLevelFiles(level);
       if (stats_[level].micros > 0 || files > 0) {
-        snprintf(
-            buf, sizeof(buf),
-            "%3d %8d %8.0f %9.0f %8.0f %9.0f\n",
-            level,
-            files,
-            versions_->NumLevelBytes(level) / 1048576.0,
-            stats_[level].micros / 1e6,
-            stats_[level].bytes_read / 1048576.0,
-            stats_[level].bytes_written / 1048576.0);
+        snprintf(buf, sizeof(buf), "%3d %8d %8.0f %9.0f %8.0f %9.0f\n", level,
+                 files, versions_->NumLevelBytes(level) / 1048576.0,
+                 stats_[level].micros / 1e6,
+                 stats_[level].bytes_read / 1048576.0,
+                 stats_[level].bytes_written / 1048576.0);
         value->append(buf);
       }
     }
@@ -1406,21 +1422,29 @@ bool DBImpl::GetProperty(const Slice& property, std::string* value) {
   } else if (in == "sstables") {
     *value = versions_->current()->DebugString();
     return true;
+  } else if (in == "approximate-memory-usage") {
+    size_t total_usage = options_.block_cache->TotalCharge();
+    if (mem_) {
+      total_usage += mem_->ApproximateMemoryUsage();
+    }
+    if (imm_) {
+      total_usage += imm_->ApproximateMemoryUsage();
+    }
+    char buf[50];
+    snprintf(buf, sizeof(buf), "%llu",
+             static_cast<unsigned long long>(total_usage));
+    value->append(buf);
+    return true;
   }
 
   return false;
 }
 
-void DBImpl::GetApproximateSizes(
-    const Range* range, int n,
-    uint64_t* sizes) {
+void DBImpl::GetApproximateSizes(const Range* range, int n, uint64_t* sizes) {
   // TODO(opt): better implementation
-  Version* v;
-  {
-    MutexLock l(&mutex_);
-    versions_->current()->Ref();
-    v = versions_->current();
-  }
+  MutexLock l(&mutex_);
+  Version* v = versions_->current();
+  v->Ref();
 
   for (int i = 0; i < n; i++) {
     // Convert user_key into a corresponding internal key.
@@ -1431,10 +1455,7 @@ void DBImpl::GetApproximateSizes(
     sizes[i] = (limit >= start ? limit - start : 0);
   }
 
-  {
-    MutexLock l(&mutex_);
-    v->Unref();
-  }
+  v->Unref();
 }
 
 // Default implementations of convenience methods that subclasses of DB
@@ -1451,17 +1472,19 @@ Status DB::Delete(const WriteOptions& opt, const Slice& key) {
   return Write(opt, &batch);
 }
 
-DB::~DB() { }
+DB::~DB() = default;
 
-Status DB::Open(const Options& options, const std::string& dbname,
-                DB** dbptr) {
-  *dbptr = NULL;
+Status DB::Open(const Options& options, const std::string& dbname, DB** dbptr) {
+  *dbptr = nullptr;
 
   DBImpl* impl = new DBImpl(options, dbname);
   impl->mutex_.Lock();
   VersionEdit edit;
-  Status s = impl->Recover(&edit); // Handles create_if_missing, error_if_exists
-  if (s.ok()) {
+  // Recover handles create_if_missing, error_if_exists
+  bool save_manifest = false;
+  Status s = impl->Recover(&edit, &save_manifest);
+  if (s.ok() && impl->mem_ == nullptr) {
+    // Create new log and a corresponding memtable.
     uint64_t new_log_number = impl->versions_->NewFileNumber();
     WritableFile* lfile;
     s = options.env->NewWritableFile(LogFileName(dbname, new_log_number),
@@ -1471,15 +1494,22 @@ Status DB::Open(const Options& options, const std::string& dbname,
       impl->logfile_ = lfile;
       impl->logfile_number_ = new_log_number;
       impl->log_ = new log::Writer(lfile);
-      s = impl->versions_->LogAndApply(&edit, &impl->mutex_);
-    }
-    if (s.ok()) {
-      impl->DeleteObsoleteFiles();
-      impl->MaybeScheduleCompaction();
+      impl->mem_ = new MemTable(impl->internal_comparator_);
+      impl->mem_->Ref();
     }
   }
+  if (s.ok() && save_manifest) {
+    edit.SetPrevLogNumber(0);  // No older logs needed after recovery.
+    edit.SetLogNumber(impl->logfile_number_);
+    s = impl->versions_->LogAndApply(&edit, &impl->mutex_);
+  }
+  if (s.ok()) {
+    impl->DeleteObsoleteFiles();
+    impl->MaybeScheduleCompaction();
+  }
   impl->mutex_.Unlock();
   if (s.ok()) {
+    assert(impl->mem_ != nullptr);
     *dbptr = impl;
   } else {
     delete impl;
@@ -1487,21 +1517,20 @@ Status DB::Open(const Options& options, const std::string& dbname,
   return s;
 }
 
-Snapshot::~Snapshot() {
-}
+Snapshot::~Snapshot() = default;
 
 Status DestroyDB(const std::string& dbname, const Options& options) {
   Env* env = options.env;
   std::vector<std::string> filenames;
-  // Ignore error in case directory does not exist
-  env->GetChildren(dbname, &filenames);
-  if (filenames.empty()) {
+  Status result = env->GetChildren(dbname, &filenames);
+  if (!result.ok()) {
+    // Ignore error in case directory does not exist
     return Status::OK();
   }
 
   FileLock* lock;
   const std::string lockname = LockFileName(dbname);
-  Status result = env->LockFile(lockname, &lock);
+  result = env->LockFile(lockname, &lock);
   if (result.ok()) {
     uint64_t number;
     FileType type;
diff --git a/db/db_impl.h b/db/db_impl.h
index cfc9981..685735c 100644
--- a/db/db_impl.h
+++ b/db/db_impl.h
@@ -5,8 +5,11 @@
 #ifndef STORAGE_LEVELDB_DB_DB_IMPL_H_
 #define STORAGE_LEVELDB_DB_DB_IMPL_H_
 
+#include <atomic>
 #include <deque>
 #include <set>
+#include <string>
+
 #include "db/dbformat.h"
 #include "db/log_writer.h"
 #include "db/snapshot.h"
@@ -26,21 +29,25 @@ class VersionSet;
 class DBImpl : public DB {
  public:
   DBImpl(const Options& options, const std::string& dbname);
-  virtual ~DBImpl();
+
+  DBImpl(const DBImpl&) = delete;
+  DBImpl& operator=(const DBImpl&) = delete;
+
+  ~DBImpl() override;
 
   // Implementations of the DB interface
-  virtual Status Put(const WriteOptions&, const Slice& key, const Slice& value);
-  virtual Status Delete(const WriteOptions&, const Slice& key);
-  virtual Status Write(const WriteOptions& options, WriteBatch* updates);
-  virtual Status Get(const ReadOptions& options,
-                     const Slice& key,
-                     std::string* value);
-  virtual Iterator* NewIterator(const ReadOptions&);
-  virtual const Snapshot* GetSnapshot();
-  virtual void ReleaseSnapshot(const Snapshot* snapshot);
-  virtual bool GetProperty(const Slice& property, std::string* value);
-  virtual void GetApproximateSizes(const Range* range, int n, uint64_t* sizes);
-  virtual void CompactRange(const Slice* begin, const Slice* end);
+  Status Put(const WriteOptions&, const Slice& key,
+             const Slice& value) override;
+  Status Delete(const WriteOptions&, const Slice& key) override;
+  Status Write(const WriteOptions& options, WriteBatch* updates) override;
+  Status Get(const ReadOptions& options, const Slice& key,
+             std::string* value) override;
+  Iterator* NewIterator(const ReadOptions&) override;
+  const Snapshot* GetSnapshot() override;
+  void ReleaseSnapshot(const Snapshot* snapshot) override;
+  bool GetProperty(const Slice& property, std::string* value) override;
+  void GetApproximateSizes(const Range* range, int n, uint64_t* sizes) override;
+  void CompactRange(const Slice* begin, const Slice* end) override;
 
   // Extra methods (for testing) that are not in the public DB interface
 
@@ -69,6 +76,31 @@ class DBImpl : public DB {
   struct CompactionState;
   struct Writer;
 
+  // Information for a manual compaction
+  struct ManualCompaction {
+    int level;
+    bool done;
+    const InternalKey* begin;  // null means beginning of key range
+    const InternalKey* end;    // null means end of key range
+    InternalKey tmp_storage;   // Used to keep track of compaction progress
+  };
+
+  // Per level compaction stats.  stats_[level] stores the stats for
+  // compactions that produced data for the specified "level".
+  struct CompactionStats {
+    CompactionStats() : micros(0), bytes_read(0), bytes_written(0) {}
+
+    void Add(const CompactionStats& c) {
+      this->micros += c.micros;
+      this->bytes_read += c.bytes_read;
+      this->bytes_written += c.bytes_written;
+    }
+
+    int64_t micros;
+    int64_t bytes_read;
+    int64_t bytes_written;
+  };
+
   Iterator* NewInternalIterator(const ReadOptions&,
                                 SequenceNumber* latest_snapshot,
                                 uint32_t* seed);
@@ -78,21 +110,21 @@ class DBImpl : public DB {
   // Recover the descriptor from persistent storage.  May do a significant
   // amount of work to recover recently logged updates.  Any changes to
   // be made to the descriptor are added to *edit.
-  Status Recover(VersionEdit* edit) EXCLUSIVE_LOCKS_REQUIRED(mutex_);
+  Status Recover(VersionEdit* edit, bool* save_manifest)
+      EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
   void MaybeIgnoreError(Status* s) const;
 
   // Delete any unneeded files and stale in-memory entries.
-  void DeleteObsoleteFiles();
+  void DeleteObsoleteFiles() EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
   // Compact the in-memory write buffer to disk.  Switches to a new
   // log-file/memtable and writes a new descriptor iff successful.
   // Errors are recorded in bg_error_.
   void CompactMemTable() EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
-  Status RecoverLogFile(uint64_t log_number,
-                        VersionEdit* edit,
-                        SequenceNumber* max_sequence)
+  Status RecoverLogFile(uint64_t log_number, bool last_log, bool* save_manifest,
+                        VersionEdit* edit, SequenceNumber* max_sequence)
       EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
   Status WriteLevel0Table(MemTable* mem, VersionEdit* edit, Version* base)
@@ -100,14 +132,15 @@ class DBImpl : public DB {
 
   Status MakeRoomForWrite(bool force /* compact even if there is room? */)
       EXCLUSIVE_LOCKS_REQUIRED(mutex_);
-  WriteBatch* BuildBatchGroup(Writer** last_writer);
+  WriteBatch* BuildBatchGroup(Writer** last_writer)
+      EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
   void RecordBackgroundError(const Status& s);
 
   void MaybeScheduleCompaction() EXCLUSIVE_LOCKS_REQUIRED(mutex_);
   static void BGWork(void* db);
   void BackgroundCall();
-  void  BackgroundCompaction() EXCLUSIVE_LOCKS_REQUIRED(mutex_);
+  void BackgroundCompaction() EXCLUSIVE_LOCKS_REQUIRED(mutex_);
   void CleanupCompaction(CompactionState* compact)
       EXCLUSIVE_LOCKS_REQUIRED(mutex_);
   Status DoCompactionWork(CompactionState* compact)
@@ -118,93 +151,66 @@ class DBImpl : public DB {
   Status InstallCompactionResults(CompactionState* compact)
       EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
+  const Comparator* user_comparator() const {
+    return internal_comparator_.user_comparator();
+  }
+
   // Constant after construction
   Env* const env_;
   const InternalKeyComparator internal_comparator_;
   const InternalFilterPolicy internal_filter_policy_;
   const Options options_;  // options_.comparator == &internal_comparator_
-  bool owns_info_log_;
-  bool owns_cache_;
+  const bool owns_info_log_;
+  const bool owns_cache_;
   const std::string dbname_;
 
   // table_cache_ provides its own synchronization
-  TableCache* table_cache_;
+  TableCache* const table_cache_;
 
-  // Lock over the persistent DB state.  Non-NULL iff successfully acquired.
+  // Lock over the persistent DB state.  Non-null iff successfully acquired.
   FileLock* db_lock_;
 
   // State below is protected by mutex_
   port::Mutex mutex_;
-  port::AtomicPointer shutting_down_;
-  port::CondVar bg_cv_;          // Signalled when background work finishes
+  std::atomic<bool> shutting_down_;
+  port::CondVar background_work_finished_signal_ GUARDED_BY(mutex_);
   MemTable* mem_;
-  MemTable* imm_;                // Memtable being compacted
-  port::AtomicPointer has_imm_;  // So bg thread can detect non-NULL imm_
+  MemTable* imm_ GUARDED_BY(mutex_);  // Memtable being compacted
+  std::atomic<bool> has_imm_;         // So bg thread can detect non-null imm_
   WritableFile* logfile_;
-  uint64_t logfile_number_;
+  uint64_t logfile_number_ GUARDED_BY(mutex_);
   log::Writer* log_;
-  uint32_t seed_;                // For sampling.
+  uint32_t seed_ GUARDED_BY(mutex_);  // For sampling.
 
   // Queue of writers.
-  std::deque<Writer*> writers_;
-  WriteBatch* tmp_batch_;
+  std::deque<Writer*> writers_ GUARDED_BY(mutex_);
+  WriteBatch* tmp_batch_ GUARDED_BY(mutex_);
 
-  SnapshotList snapshots_;
+  SnapshotList snapshots_ GUARDED_BY(mutex_);
 
   // Set of table files to protect from deletion because they are
   // part of ongoing compactions.
-  std::set<uint64_t> pending_outputs_;
+  std::set<uint64_t> pending_outputs_ GUARDED_BY(mutex_);
 
   // Has a background compaction been scheduled or is running?
-  bool bg_compaction_scheduled_;
+  bool background_compaction_scheduled_ GUARDED_BY(mutex_);
 
-  // Information for a manual compaction
-  struct ManualCompaction {
-    int level;
-    bool done;
-    const InternalKey* begin;   // NULL means beginning of key range
-    const InternalKey* end;     // NULL means end of key range
-    InternalKey tmp_storage;    // Used to keep track of compaction progress
-  };
-  ManualCompaction* manual_compaction_;
+  ManualCompaction* manual_compaction_ GUARDED_BY(mutex_);
 
-  VersionSet* versions_;
+  VersionSet* const versions_ GUARDED_BY(mutex_);
 
   // Have we encountered a background error in paranoid mode?
-  Status bg_error_;
+  Status bg_error_ GUARDED_BY(mutex_);
 
-  // Per level compaction stats.  stats_[level] stores the stats for
-  // compactions that produced data for the specified "level".
-  struct CompactionStats {
-    int64_t micros;
-    int64_t bytes_read;
-    int64_t bytes_written;
-
-    CompactionStats() : micros(0), bytes_read(0), bytes_written(0) { }
-
-    void Add(const CompactionStats& c) {
-      this->micros += c.micros;
-      this->bytes_read += c.bytes_read;
-      this->bytes_written += c.bytes_written;
-    }
-  };
-  CompactionStats stats_[config::kNumLevels];
-
-  // No copying allowed
-  DBImpl(const DBImpl&);
-  void operator=(const DBImpl&);
-
-  const Comparator* user_comparator() const {
-    return internal_comparator_.user_comparator();
-  }
+  CompactionStats stats_[config::kNumLevels] GUARDED_BY(mutex_);
 };
 
 // Sanitize db options.  The caller should delete result.info_log if
 // it is not equal to src.info_log.
-extern Options SanitizeOptions(const std::string& db,
-                               const InternalKeyComparator* icmp,
-                               const InternalFilterPolicy* ipolicy,
-                               const Options& src);
+Options SanitizeOptions(const std::string& db,
+                        const InternalKeyComparator* icmp,
+                        const InternalFilterPolicy* ipolicy,
+                        const Options& src);
 
 }  // namespace leveldb
 
diff --git a/db/db_iter.cc b/db/db_iter.cc
index 3b2035e..98715a9 100644
--- a/db/db_iter.cc
+++ b/db/db_iter.cc
@@ -4,9 +4,9 @@
 
 #include "db/db_iter.h"
 
-#include "db/filename.h"
 #include "db/db_impl.h"
 #include "db/dbformat.h"
+#include "db/filename.h"
 #include "leveldb/env.h"
 #include "leveldb/iterator.h"
 #include "port/port.h"
@@ -36,17 +36,14 @@ namespace {
 // combines multiple entries for the same userkey found in the DB
 // representation into a single entry while accounting for sequence
 // numbers, deletion markers, overwrites, etc.
-class DBIter: public Iterator {
+class DBIter : public Iterator {
  public:
   // Which direction is the iterator currently moving?
   // (1) When moving forward, the internal iterator is positioned at
   //     the exact entry that yields this->key(), this->value()
   // (2) When moving backwards, the internal iterator is positioned
   //     just before all entries whose user key == this->key().
-  enum Direction {
-    kForward,
-    kReverse
-  };
+  enum Direction { kForward, kReverse };
 
   DBIter(DBImpl* db, const Comparator* cmp, Iterator* iter, SequenceNumber s,
          uint32_t seed)
@@ -57,21 +54,22 @@ class DBIter: public Iterator {
         direction_(kForward),
         valid_(false),
         rnd_(seed),
-        bytes_counter_(RandomPeriod()) {
-  }
-  virtual ~DBIter() {
-    delete iter_;
-  }
-  virtual bool Valid() const { return valid_; }
-  virtual Slice key() const {
+        bytes_until_read_sampling_(RandomCompactionPeriod()) {}
+
+  DBIter(const DBIter&) = delete;
+  DBIter& operator=(const DBIter&) = delete;
+
+  ~DBIter() override { delete iter_; }
+  bool Valid() const override { return valid_; }
+  Slice key() const override {
     assert(valid_);
     return (direction_ == kForward) ? ExtractUserKey(iter_->key()) : saved_key_;
   }
-  virtual Slice value() const {
+  Slice value() const override {
     assert(valid_);
     return (direction_ == kForward) ? iter_->value() : saved_value_;
   }
-  virtual Status status() const {
+  Status status() const override {
     if (status_.ok()) {
       return iter_->status();
     } else {
@@ -79,11 +77,11 @@ class DBIter: public Iterator {
     }
   }
 
-  virtual void Next();
-  virtual void Prev();
-  virtual void Seek(const Slice& target);
-  virtual void SeekToFirst();
-  virtual void SeekToLast();
+  void Next() override;
+  void Prev() override;
+  void Seek(const Slice& target) override;
+  void SeekToFirst() override;
+  void SeekToLast() override;
 
  private:
   void FindNextUserEntry(bool skipping, std::string* skip);
@@ -103,38 +101,35 @@ class DBIter: public Iterator {
     }
   }
 
-  // Pick next gap with average value of config::kReadBytesPeriod.
-  ssize_t RandomPeriod() {
-    return rnd_.Uniform(2*config::kReadBytesPeriod);
+  // Picks the number of bytes that can be read until a compaction is scheduled.
+  size_t RandomCompactionPeriod() {
+    return rnd_.Uniform(2 * config::kReadBytesPeriod);
   }
 
   DBImpl* db_;
   const Comparator* const user_comparator_;
   Iterator* const iter_;
   SequenceNumber const sequence_;
-
   Status status_;
-  std::string saved_key_;     // == current key when direction_==kReverse
-  std::string saved_value_;   // == current raw value when direction_==kReverse
+  std::string saved_key_;    // == current key when direction_==kReverse
+  std::string saved_value_;  // == current raw value when direction_==kReverse
   Direction direction_;
   bool valid_;
-
   Random rnd_;
-  ssize_t bytes_counter_;
-
-  // No copying allowed
-  DBIter(const DBIter&);
-  void operator=(const DBIter&);
+  size_t bytes_until_read_sampling_;
 };
 
 inline bool DBIter::ParseKey(ParsedInternalKey* ikey) {
   Slice k = iter_->key();
-  ssize_t n = k.size() + iter_->value().size();
-  bytes_counter_ -= n;
-  while (bytes_counter_ < 0) {
-    bytes_counter_ += RandomPeriod();
+
+  size_t bytes_read = k.size() + iter_->value().size();
+  while (bytes_until_read_sampling_ < bytes_read) {
+    bytes_until_read_sampling_ += RandomCompactionPeriod();
     db_->RecordReadSample(k);
   }
+  assert(bytes_until_read_sampling_ >= bytes_read);
+  bytes_until_read_sampling_ -= bytes_read;
+
   if (!ParseInternalKey(k, ikey)) {
     status_ = Status::Corruption("corrupted internal key in DBIter");
     return false;
@@ -165,6 +160,15 @@ void DBIter::Next() {
   } else {
     // Store in saved_key_ the current key so we skip it below.
     SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
+
+    // iter_ is pointing to current key. We can now safely move to the next to
+    // avoid checking current key.
+    iter_->Next();
+    if (!iter_->Valid()) {
+      valid_ = false;
+      saved_key_.clear();
+      return;
+    }
   }
 
   FindNextUserEntry(true, &saved_key_);
@@ -218,8 +222,8 @@ void DBIter::Prev() {
         ClearSavedValue();
         return;
       }
-      if (user_comparator_->Compare(ExtractUserKey(iter_->key()),
-                                    saved_key_) < 0) {
+      if (user_comparator_->Compare(ExtractUserKey(iter_->key()), saved_key_) <
+          0) {
         break;
       }
     }
@@ -275,8 +279,8 @@ void DBIter::Seek(const Slice& target) {
   direction_ = kForward;
   ClearSavedValue();
   saved_key_.clear();
-  AppendInternalKey(
-      &saved_key_, ParsedInternalKey(target, sequence_, kValueTypeForSeek));
+  AppendInternalKey(&saved_key_,
+                    ParsedInternalKey(target, sequence_, kValueTypeForSeek));
   iter_->Seek(saved_key_);
   if (iter_->Valid()) {
     FindNextUserEntry(false, &saved_key_ /* temporary storage */);
@@ -305,12 +309,9 @@ void DBIter::SeekToLast() {
 
 }  // anonymous namespace
 
-Iterator* NewDBIterator(
-    DBImpl* db,
-    const Comparator* user_key_comparator,
-    Iterator* internal_iter,
-    SequenceNumber sequence,
-    uint32_t seed) {
+Iterator* NewDBIterator(DBImpl* db, const Comparator* user_key_comparator,
+                        Iterator* internal_iter, SequenceNumber sequence,
+                        uint32_t seed) {
   return new DBIter(db, user_key_comparator, internal_iter, sequence, seed);
 }
 
diff --git a/db/db_iter.h b/db/db_iter.h
index 04927e9..fd93e91 100644
--- a/db/db_iter.h
+++ b/db/db_iter.h
@@ -6,8 +6,9 @@
 #define STORAGE_LEVELDB_DB_DB_ITER_H_
 
 #include <stdint.h>
-#include "leveldb/db.h"
+
 #include "db/dbformat.h"
+#include "leveldb/db.h"
 
 namespace leveldb {
 
@@ -16,12 +17,9 @@ class DBImpl;
 // Return a new iterator that converts internal keys (yielded by
 // "*internal_iter") that were live at the specified "sequence" number
 // into appropriate user keys.
-extern Iterator* NewDBIterator(
-    DBImpl* db,
-    const Comparator* user_key_comparator,
-    Iterator* internal_iter,
-    SequenceNumber sequence,
-    uint32_t seed);
+Iterator* NewDBIterator(DBImpl* db, const Comparator* user_key_comparator,
+                        Iterator* internal_iter, SequenceNumber sequence,
+                        uint32_t seed);
 
 }  // namespace leveldb
 
diff --git a/db/db_test.cc b/db/db_test.cc
index 0fed913..9a8faf1 100644
--- a/db/db_test.cc
+++ b/db/db_test.cc
@@ -3,14 +3,20 @@
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
 #include "leveldb/db.h"
-#include "leveldb/filter_policy.h"
+
+#include <atomic>
+#include <string>
+
 #include "db/db_impl.h"
 #include "db/filename.h"
 #include "db/version_set.h"
 #include "db/write_batch_internal.h"
 #include "leveldb/cache.h"
 #include "leveldb/env.h"
+#include "leveldb/filter_policy.h"
 #include "leveldb/table.h"
+#include "port/port.h"
+#include "port/thread_annotations.h"
 #include "util/hash.h"
 #include "util/logging.h"
 #include "util/mutexlock.h"
@@ -25,83 +31,116 @@ static std::string RandomString(Random* rnd, int len) {
   return r;
 }
 
+static std::string RandomKey(Random* rnd) {
+  int len =
+      (rnd->OneIn(3) ? 1  // Short sometimes to encourage collisions
+                     : (rnd->OneIn(100) ? rnd->Skewed(10) : rnd->Uniform(10)));
+  return test::RandomKey(rnd, len);
+}
+
 namespace {
 class AtomicCounter {
- private:
-  port::Mutex mu_;
-  int count_;
  public:
-  AtomicCounter() : count_(0) { }
-  void Increment() {
-    IncrementBy(1);
-  }
-  void IncrementBy(int count) {
+  AtomicCounter() : count_(0) {}
+  void Increment() { IncrementBy(1); }
+  void IncrementBy(int count) LOCKS_EXCLUDED(mu_) {
     MutexLock l(&mu_);
     count_ += count;
   }
-  int Read() {
+  int Read() LOCKS_EXCLUDED(mu_) {
     MutexLock l(&mu_);
     return count_;
   }
-  void Reset() {
+  void Reset() LOCKS_EXCLUDED(mu_) {
     MutexLock l(&mu_);
     count_ = 0;
   }
+
+ private:
+  port::Mutex mu_;
+  int count_ GUARDED_BY(mu_);
 };
 
 void DelayMilliseconds(int millis) {
   Env::Default()->SleepForMicroseconds(millis * 1000);
 }
-}
+}  // namespace
 
-// Special Env used to delay background operations
+// Test Env to override default Env behavior for testing.
+class TestEnv : public EnvWrapper {
+ public:
+  explicit TestEnv(Env* base) : EnvWrapper(base), ignore_dot_files_(false) {}
+
+  void SetIgnoreDotFiles(bool ignored) { ignore_dot_files_ = ignored; }
+
+  Status GetChildren(const std::string& dir,
+                     std::vector<std::string>* result) override {
+    Status s = target()->GetChildren(dir, result);
+    if (!s.ok() || !ignore_dot_files_) {
+      return s;
+    }
+
+    std::vector<std::string>::iterator it = result->begin();
+    while (it != result->end()) {
+      if ((*it == ".") || (*it == "..")) {
+        it = result->erase(it);
+      } else {
+        ++it;
+      }
+    }
+
+    return s;
+  }
+
+ private:
+  bool ignore_dot_files_;
+};
+
+// Special Env used to delay background operations.
 class SpecialEnv : public EnvWrapper {
  public:
-  // sstable/log Sync() calls are blocked while this pointer is non-NULL.
-  port::AtomicPointer delay_data_sync_;
+  // sstable/log Sync() calls are blocked while this pointer is non-null.
+  std::atomic<bool> delay_data_sync_;
 
   // sstable/log Sync() calls return an error.
-  port::AtomicPointer data_sync_error_;
+  std::atomic<bool> data_sync_error_;
 
-  // Simulate no-space errors while this pointer is non-NULL.
-  port::AtomicPointer no_space_;
+  // Simulate no-space errors while this pointer is non-null.
+  std::atomic<bool> no_space_;
 
-  // Simulate non-writable file system while this pointer is non-NULL
-  port::AtomicPointer non_writable_;
+  // Simulate non-writable file system while this pointer is non-null.
+  std::atomic<bool> non_writable_;
 
-  // Force sync of manifest files to fail while this pointer is non-NULL
-  port::AtomicPointer manifest_sync_error_;
+  // Force sync of manifest files to fail while this pointer is non-null.
+  std::atomic<bool> manifest_sync_error_;
 
-  // Force write to manifest files to fail while this pointer is non-NULL
-  port::AtomicPointer manifest_write_error_;
+  // Force write to manifest files to fail while this pointer is non-null.
+  std::atomic<bool> manifest_write_error_;
 
   bool count_random_reads_;
   AtomicCounter random_read_counter_;
 
-  explicit SpecialEnv(Env* base) : EnvWrapper(base) {
-    delay_data_sync_.Release_Store(NULL);
-    data_sync_error_.Release_Store(NULL);
-    no_space_.Release_Store(NULL);
-    non_writable_.Release_Store(NULL);
-    count_random_reads_ = false;
-    manifest_sync_error_.Release_Store(NULL);
-    manifest_write_error_.Release_Store(NULL);
-  }
+  explicit SpecialEnv(Env* base)
+      : EnvWrapper(base),
+        delay_data_sync_(false),
+        data_sync_error_(false),
+        no_space_(false),
+        non_writable_(false),
+        manifest_sync_error_(false),
+        manifest_write_error_(false),
+        count_random_reads_(false) {}
 
   Status NewWritableFile(const std::string& f, WritableFile** r) {
     class DataFile : public WritableFile {
      private:
-      SpecialEnv* env_;
-      WritableFile* base_;
+      SpecialEnv* const env_;
+      WritableFile* const base_;
 
      public:
-      DataFile(SpecialEnv* env, WritableFile* base)
-          : env_(env),
-            base_(base) {
-      }
+      DataFile(SpecialEnv* env, WritableFile* base) : env_(env), base_(base) {}
       ~DataFile() { delete base_; }
       Status Append(const Slice& data) {
-        if (env_->no_space_.Acquire_Load() != NULL) {
+        if (env_->no_space_.load(std::memory_order_acquire)) {
           // Drop writes on the floor
           return Status::OK();
         } else {
@@ -111,10 +150,10 @@ class SpecialEnv : public EnvWrapper {
       Status Close() { return base_->Close(); }
       Status Flush() { return base_->Flush(); }
       Status Sync() {
-        if (env_->data_sync_error_.Acquire_Load() != NULL) {
+        if (env_->data_sync_error_.load(std::memory_order_acquire)) {
           return Status::IOError("simulated data sync error");
         }
-        while (env_->delay_data_sync_.Acquire_Load() != NULL) {
+        while (env_->delay_data_sync_.load(std::memory_order_acquire)) {
           DelayMilliseconds(100);
         }
         return base_->Sync();
@@ -124,11 +163,12 @@ class SpecialEnv : public EnvWrapper {
      private:
       SpecialEnv* env_;
       WritableFile* base_;
+
      public:
-      ManifestFile(SpecialEnv* env, WritableFile* b) : env_(env), base_(b) { }
+      ManifestFile(SpecialEnv* env, WritableFile* b) : env_(env), base_(b) {}
       ~ManifestFile() { delete base_; }
       Status Append(const Slice& data) {
-        if (env_->manifest_write_error_.Acquire_Load() != NULL) {
+        if (env_->manifest_write_error_.load(std::memory_order_acquire)) {
           return Status::IOError("simulated writer error");
         } else {
           return base_->Append(data);
@@ -137,7 +177,7 @@ class SpecialEnv : public EnvWrapper {
       Status Close() { return base_->Close(); }
       Status Flush() { return base_->Flush(); }
       Status Sync() {
-        if (env_->manifest_sync_error_.Acquire_Load() != NULL) {
+        if (env_->manifest_sync_error_.load(std::memory_order_acquire)) {
           return Status::IOError("simulated sync error");
         } else {
           return base_->Sync();
@@ -145,16 +185,16 @@ class SpecialEnv : public EnvWrapper {
       }
     };
 
-    if (non_writable_.Acquire_Load() != NULL) {
+    if (non_writable_.load(std::memory_order_acquire)) {
       return Status::IOError("simulated write error");
     }
 
     Status s = target()->NewWritableFile(f, r);
     if (s.ok()) {
-      if (strstr(f.c_str(), ".ldb") != NULL ||
-          strstr(f.c_str(), ".log") != NULL) {
+      if (strstr(f.c_str(), ".ldb") != nullptr ||
+          strstr(f.c_str(), ".log") != nullptr) {
         *r = new DataFile(this, *r);
-      } else if (strstr(f.c_str(), "MANIFEST") != NULL) {
+      } else if (strstr(f.c_str(), "MANIFEST") != nullptr) {
         *r = new ManifestFile(this, *r);
       }
     }
@@ -166,13 +206,13 @@ class SpecialEnv : public EnvWrapper {
      private:
       RandomAccessFile* target_;
       AtomicCounter* counter_;
+
      public:
       CountingFile(RandomAccessFile* target, AtomicCounter* counter)
-          : target_(target), counter_(counter) {
-      }
-      virtual ~CountingFile() { delete target_; }
-      virtual Status Read(uint64_t offset, size_t n, Slice* result,
-                          char* scratch) const {
+          : target_(target), counter_(counter) {}
+      ~CountingFile() override { delete target_; }
+      Status Read(uint64_t offset, size_t n, Slice* result,
+                  char* scratch) const override {
         counter_->Increment();
         return target_->Read(offset, n, result, scratch);
       }
@@ -187,18 +227,6 @@ class SpecialEnv : public EnvWrapper {
 };
 
 class DBTest {
- private:
-  const FilterPolicy* filter_policy_;
-
-  // Sequence of option configurations to try
-  enum OptionConfig {
-    kDefault,
-    kFilter,
-    kUncompressed,
-    kEnd
-  };
-  int option_config_;
-
  public:
   std::string dbname_;
   SpecialEnv* env_;
@@ -206,12 +234,11 @@ class DBTest {
 
   Options last_options_;
 
-  DBTest() : option_config_(kDefault),
-             env_(new SpecialEnv(Env::Default())) {
+  DBTest() : env_(new SpecialEnv(Env::Default())), option_config_(kDefault) {
     filter_policy_ = NewBloomFilterPolicy(10);
     dbname_ = test::TmpDir() + "/db_test";
     DestroyDB(dbname_, Options());
-    db_ = NULL;
+    db_ = nullptr;
     Reopen();
   }
 
@@ -237,7 +264,11 @@ class DBTest {
   // Return the current option configuration.
   Options CurrentOptions() {
     Options options;
+    options.reuse_logs = false;
     switch (option_config_) {
+      case kReuse:
+        options.reuse_logs = true;
+        break;
       case kFilter:
         options.filter_policy = filter_policy_;
         break;
@@ -250,31 +281,27 @@ class DBTest {
     return options;
   }
 
-  DBImpl* dbfull() {
-    return reinterpret_cast<DBImpl*>(db_);
-  }
+  DBImpl* dbfull() { return reinterpret_cast<DBImpl*>(db_); }
 
-  void Reopen(Options* options = NULL) {
-    ASSERT_OK(TryReopen(options));
-  }
+  void Reopen(Options* options = nullptr) { ASSERT_OK(TryReopen(options)); }
 
   void Close() {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
   }
 
-  void DestroyAndReopen(Options* options = NULL) {
+  void DestroyAndReopen(Options* options = nullptr) {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
     DestroyDB(dbname_, Options());
     ASSERT_OK(TryReopen(options));
   }
 
   Status TryReopen(Options* options) {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
     Options opts;
-    if (options != NULL) {
+    if (options != nullptr) {
       opts = *options;
     } else {
       opts = CurrentOptions();
@@ -289,11 +316,9 @@ class DBTest {
     return db_->Put(WriteOptions(), k, v);
   }
 
-  Status Delete(const std::string& k) {
-    return db_->Delete(WriteOptions(), k);
-  }
+  Status Delete(const std::string& k) { return db_->Delete(WriteOptions(), k); }
 
-  std::string Get(const std::string& k, const Snapshot* snapshot = NULL) {
+  std::string Get(const std::string& k, const Snapshot* snapshot = nullptr) {
     ReadOptions options;
     options.snapshot = snapshot;
     std::string result;
@@ -377,10 +402,9 @@ class DBTest {
 
   int NumTableFilesAtLevel(int level) {
     std::string property;
-    ASSERT_TRUE(
-        db_->GetProperty("leveldb.num-files-at-level" + NumberToString(level),
-                         &property));
-    return atoi(property.c_str());
+    ASSERT_TRUE(db_->GetProperty(
+        "leveldb.num-files-at-level" + NumberToString(level), &property));
+    return std::stoi(property);
   }
 
   int TotalTableFiles() {
@@ -426,11 +450,12 @@ class DBTest {
   }
 
   // Do n memtable compactions, each of which produces an sstable
-  // covering the range [small,large].
-  void MakeTables(int n, const std::string& small, const std::string& large) {
+  // covering the range [small_key,large_key].
+  void MakeTables(int n, const std::string& small_key,
+                  const std::string& large_key) {
     for (int i = 0; i < n; i++) {
-      Put(small, "begin");
-      Put(large, "end");
+      Put(small_key, "begin");
+      Put(large_key, "end");
       dbfull()->TEST_CompactMemTable();
     }
   }
@@ -443,9 +468,9 @@ class DBTest {
 
   void DumpFileCounts(const char* label) {
     fprintf(stderr, "---\n%s:\n", label);
-    fprintf(stderr, "maxoverlap: %lld\n",
-            static_cast<long long>(
-                dbfull()->TEST_MaxNextLevelOverlappingBytes()));
+    fprintf(
+        stderr, "maxoverlap: %lld\n",
+        static_cast<long long>(dbfull()->TEST_MaxNextLevelOverlappingBytes()));
     for (int level = 0; level < config::kNumLevels; level++) {
       int num = NumTableFilesAtLevel(level);
       if (num > 0) {
@@ -501,15 +526,42 @@ class DBTest {
     }
     return files_renamed;
   }
+
+ private:
+  // Sequence of option configurations to try
+  enum OptionConfig { kDefault, kReuse, kFilter, kUncompressed, kEnd };
+
+  const FilterPolicy* filter_policy_;
+  int option_config_;
 };
 
 TEST(DBTest, Empty) {
   do {
-    ASSERT_TRUE(db_ != NULL);
+    ASSERT_TRUE(db_ != nullptr);
     ASSERT_EQ("NOT_FOUND", Get("foo"));
   } while (ChangeOptions());
 }
 
+TEST(DBTest, EmptyKey) {
+  do {
+    ASSERT_OK(Put("", "v1"));
+    ASSERT_EQ("v1", Get(""));
+    ASSERT_OK(Put("", "v2"));
+    ASSERT_EQ("v2", Get(""));
+  } while (ChangeOptions());
+}
+
+TEST(DBTest, EmptyValue) {
+  do {
+    ASSERT_OK(Put("key", "v1"));
+    ASSERT_EQ("v1", Get("key"));
+    ASSERT_OK(Put("key", ""));
+    ASSERT_EQ("", Get("key"));
+    ASSERT_OK(Put("key", "v2"));
+    ASSERT_EQ("v2", Get("key"));
+  } while (ChangeOptions());
+}
+
 TEST(DBTest, ReadWrite) {
   do {
     ASSERT_OK(Put("foo", "v1"));
@@ -542,11 +594,13 @@ TEST(DBTest, GetFromImmutableLayer) {
     ASSERT_OK(Put("foo", "v1"));
     ASSERT_EQ("v1", Get("foo"));
 
-    env_->delay_data_sync_.Release_Store(env_);      // Block sync calls
-    Put("k1", std::string(100000, 'x'));             // Fill memtable
-    Put("k2", std::string(100000, 'y'));             // Trigger compaction
+    // Block sync calls.
+    env_->delay_data_sync_.store(true, std::memory_order_release);
+    Put("k1", std::string(100000, 'x'));  // Fill memtable.
+    Put("k2", std::string(100000, 'y'));  // Trigger compaction.
     ASSERT_EQ("v1", Get("foo"));
-    env_->delay_data_sync_.Release_Store(NULL);      // Release sync calls
+    // Release sync calls.
+    env_->delay_data_sync_.store(false, std::memory_order_release);
   } while (ChangeOptions());
 }
 
@@ -558,6 +612,17 @@ TEST(DBTest, GetFromVersions) {
   } while (ChangeOptions());
 }
 
+TEST(DBTest, GetMemUsage) {
+  do {
+    ASSERT_OK(Put("foo", "v1"));
+    std::string val;
+    ASSERT_TRUE(db_->GetProperty("leveldb.approximate-memory-usage", &val));
+    int mem_usage = std::stoi(val);
+    ASSERT_GT(mem_usage, 0);
+    ASSERT_LT(mem_usage, 5 * 1024 * 1024);
+  } while (ChangeOptions());
+}
+
 TEST(DBTest, GetSnapshot) {
   do {
     // Try with both a short key and a long key
@@ -576,6 +641,55 @@ TEST(DBTest, GetSnapshot) {
   } while (ChangeOptions());
 }
 
+TEST(DBTest, GetIdenticalSnapshots) {
+  do {
+    // Try with both a short key and a long key
+    for (int i = 0; i < 2; i++) {
+      std::string key = (i == 0) ? std::string("foo") : std::string(200, 'x');
+      ASSERT_OK(Put(key, "v1"));
+      const Snapshot* s1 = db_->GetSnapshot();
+      const Snapshot* s2 = db_->GetSnapshot();
+      const Snapshot* s3 = db_->GetSnapshot();
+      ASSERT_OK(Put(key, "v2"));
+      ASSERT_EQ("v2", Get(key));
+      ASSERT_EQ("v1", Get(key, s1));
+      ASSERT_EQ("v1", Get(key, s2));
+      ASSERT_EQ("v1", Get(key, s3));
+      db_->ReleaseSnapshot(s1);
+      dbfull()->TEST_CompactMemTable();
+      ASSERT_EQ("v2", Get(key));
+      ASSERT_EQ("v1", Get(key, s2));
+      db_->ReleaseSnapshot(s2);
+      ASSERT_EQ("v1", Get(key, s3));
+      db_->ReleaseSnapshot(s3);
+    }
+  } while (ChangeOptions());
+}
+
+TEST(DBTest, IterateOverEmptySnapshot) {
+  do {
+    const Snapshot* snapshot = db_->GetSnapshot();
+    ReadOptions read_options;
+    read_options.snapshot = snapshot;
+    ASSERT_OK(Put("foo", "v1"));
+    ASSERT_OK(Put("foo", "v2"));
+
+    Iterator* iterator1 = db_->NewIterator(read_options);
+    iterator1->SeekToFirst();
+    ASSERT_TRUE(!iterator1->Valid());
+    delete iterator1;
+
+    dbfull()->TEST_CompactMemTable();
+
+    Iterator* iterator2 = db_->NewIterator(read_options);
+    iterator2->SeekToFirst();
+    ASSERT_TRUE(!iterator2->Valid());
+    delete iterator2;
+
+    db_->ReleaseSnapshot(snapshot);
+  } while (ChangeOptions());
+}
+
 TEST(DBTest, GetLevel0Ordering) {
   do {
     // Check that we process level-0 files in correct order.  The code
@@ -630,8 +744,7 @@ TEST(DBTest, GetEncountersEmptyLevel) {
 
     // Step 1: First place sstables in levels 0 and 2
     int compaction_count = 0;
-    while (NumTableFilesAtLevel(0) == 0 ||
-           NumTableFilesAtLevel(2) == 0) {
+    while (NumTableFilesAtLevel(0) == 0 || NumTableFilesAtLevel(2) == 0) {
       ASSERT_LE(compaction_count, 100) << "could not fill levels 0 and 2";
       compaction_count++;
       Put("a", "begin");
@@ -640,7 +753,7 @@ TEST(DBTest, GetEncountersEmptyLevel) {
     }
 
     // Step 2: clear level 1 if necessary.
-    dbfull()->TEST_CompactRange(1, NULL, NULL);
+    dbfull()->TEST_CompactRange(1, nullptr, nullptr);
     ASSERT_EQ(NumTableFilesAtLevel(0), 1);
     ASSERT_EQ(NumTableFilesAtLevel(1), 0);
     ASSERT_EQ(NumTableFilesAtLevel(2), 1);
@@ -768,10 +881,10 @@ TEST(DBTest, IterMulti) {
   ASSERT_EQ(IterStatus(iter), "b->vb");
 
   // Make sure iter stays at snapshot
-  ASSERT_OK(Put("a",  "va2"));
+  ASSERT_OK(Put("a", "va2"));
   ASSERT_OK(Put("a2", "va3"));
-  ASSERT_OK(Put("b",  "vb2"));
-  ASSERT_OK(Put("c",  "vc2"));
+  ASSERT_OK(Put("b", "vb2"));
+  ASSERT_OK(Put("c", "vc2"));
   ASSERT_OK(Delete("b"));
   iter->SeekToFirst();
   ASSERT_EQ(IterStatus(iter), "a->va");
@@ -962,7 +1075,7 @@ TEST(DBTest, RecoverWithLargeLog) {
 
 TEST(DBTest, CompactionsGenerateMultipleFiles) {
   Options options = CurrentOptions();
-  options.write_buffer_size = 100000000;        // Large write buffer
+  options.write_buffer_size = 100000000;  // Large write buffer
   Reopen(&options);
 
   Random rnd(301);
@@ -977,7 +1090,7 @@ TEST(DBTest, CompactionsGenerateMultipleFiles) {
 
   // Reopening moves updates to level-0
   Reopen(&options);
-  dbfull()->TEST_CompactRange(0, NULL, NULL);
+  dbfull()->TEST_CompactRange(0, nullptr, nullptr);
 
   ASSERT_EQ(NumTableFilesAtLevel(0), 0);
   ASSERT_GT(NumTableFilesAtLevel(1), 1);
@@ -1001,7 +1114,7 @@ TEST(DBTest, RepeatedWritesToSameKey) {
   for (int i = 0; i < 5 * kMaxFiles; i++) {
     Put("key", value);
     ASSERT_LE(TotalTableFiles(), kMaxFiles);
-    fprintf(stderr, "after %d: %d files\n", int(i+1), TotalTableFiles());
+    fprintf(stderr, "after %d: %d files\n", i + 1, TotalTableFiles());
   }
 }
 
@@ -1028,29 +1141,28 @@ TEST(DBTest, SparseMerge) {
   }
   Put("C", "vc");
   dbfull()->TEST_CompactMemTable();
-  dbfull()->TEST_CompactRange(0, NULL, NULL);
+  dbfull()->TEST_CompactRange(0, nullptr, nullptr);
 
   // Make sparse update
-  Put("A",    "va2");
+  Put("A", "va2");
   Put("B100", "bvalue2");
-  Put("C",    "vc2");
+  Put("C", "vc2");
   dbfull()->TEST_CompactMemTable();
 
   // Compactions should not cause us to create a situation where
   // a file overlaps too much data at the next level.
-  ASSERT_LE(dbfull()->TEST_MaxNextLevelOverlappingBytes(), 20*1048576);
-  dbfull()->TEST_CompactRange(0, NULL, NULL);
-  ASSERT_LE(dbfull()->TEST_MaxNextLevelOverlappingBytes(), 20*1048576);
-  dbfull()->TEST_CompactRange(1, NULL, NULL);
-  ASSERT_LE(dbfull()->TEST_MaxNextLevelOverlappingBytes(), 20*1048576);
+  ASSERT_LE(dbfull()->TEST_MaxNextLevelOverlappingBytes(), 20 * 1048576);
+  dbfull()->TEST_CompactRange(0, nullptr, nullptr);
+  ASSERT_LE(dbfull()->TEST_MaxNextLevelOverlappingBytes(), 20 * 1048576);
+  dbfull()->TEST_CompactRange(1, nullptr, nullptr);
+  ASSERT_LE(dbfull()->TEST_MaxNextLevelOverlappingBytes(), 20 * 1048576);
 }
 
 static bool Between(uint64_t val, uint64_t low, uint64_t high) {
   bool result = (val >= low) && (val <= high);
   if (!result) {
     fprintf(stderr, "Value %llu is not in range [%llu, %llu]\n",
-            (unsigned long long)(val),
-            (unsigned long long)(low),
+            (unsigned long long)(val), (unsigned long long)(low),
             (unsigned long long)(high));
   }
   return result;
@@ -1059,7 +1171,7 @@ static bool Between(uint64_t val, uint64_t low, uint64_t high) {
 TEST(DBTest, ApproximateSizes) {
   do {
     Options options = CurrentOptions();
-    options.write_buffer_size = 100000000;        // Large write buffer
+    options.write_buffer_size = 100000000;  // Large write buffer
     options.compression = kNoCompression;
     DestroyAndReopen();
 
@@ -1080,18 +1192,27 @@ TEST(DBTest, ApproximateSizes) {
     // 0 because GetApproximateSizes() does not account for memtable space
     ASSERT_TRUE(Between(Size("", Key(50)), 0, 0));
 
+    if (options.reuse_logs) {
+      // Recovery will reuse memtable, and GetApproximateSizes() does not
+      // account for memtable usage;
+      Reopen(&options);
+      ASSERT_TRUE(Between(Size("", Key(50)), 0, 0));
+      continue;
+    }
+
     // Check sizes across recovery by reopening a few times
     for (int run = 0; run < 3; run++) {
       Reopen(&options);
 
       for (int compact_start = 0; compact_start < N; compact_start += 10) {
         for (int i = 0; i < N; i += 10) {
-          ASSERT_TRUE(Between(Size("", Key(i)), S1*i, S2*i));
-          ASSERT_TRUE(Between(Size("", Key(i)+".suffix"), S1*(i+1), S2*(i+1)));
-          ASSERT_TRUE(Between(Size(Key(i), Key(i+10)), S1*10, S2*10));
+          ASSERT_TRUE(Between(Size("", Key(i)), S1 * i, S2 * i));
+          ASSERT_TRUE(Between(Size("", Key(i) + ".suffix"), S1 * (i + 1),
+                              S2 * (i + 1)));
+          ASSERT_TRUE(Between(Size(Key(i), Key(i + 10)), S1 * 10, S2 * 10));
         }
-        ASSERT_TRUE(Between(Size("", Key(50)), S1*50, S2*50));
-        ASSERT_TRUE(Between(Size("", Key(50)+".suffix"), S1*50, S2*50));
+        ASSERT_TRUE(Between(Size("", Key(50)), S1 * 50, S2 * 50));
+        ASSERT_TRUE(Between(Size("", Key(50) + ".suffix"), S1 * 50, S2 * 50));
 
         std::string cstart_str = Key(compact_start);
         std::string cend_str = Key(compact_start + 9);
@@ -1123,6 +1244,11 @@ TEST(DBTest, ApproximateSizes_MixOfSmallAndLarge) {
     ASSERT_OK(Put(Key(6), RandomString(&rnd, 300000)));
     ASSERT_OK(Put(Key(7), RandomString(&rnd, 10000)));
 
+    if (options.reuse_logs) {
+      // Need to force a memtable compaction since recovery does not do so.
+      ASSERT_OK(dbfull()->TEST_CompactMemTable());
+    }
+
     // Check sizes across recovery by reopening a few times
     for (int run = 0; run < 3; run++) {
       Reopen(&options);
@@ -1139,7 +1265,7 @@ TEST(DBTest, ApproximateSizes_MixOfSmallAndLarge) {
 
       ASSERT_TRUE(Between(Size(Key(3), Key(5)), 110000, 111000));
 
-      dbfull()->TEST_CompactRange(0, NULL, NULL);
+      dbfull()->TEST_CompactRange(0, nullptr, nullptr);
     }
   } while (ChangeOptions());
 }
@@ -1153,7 +1279,7 @@ TEST(DBTest, IteratorPinsRef) {
   // Write to force compactions
   Put("foo", "newvalue1");
   for (int i = 0; i < 100; i++) {
-    ASSERT_OK(Put(Key(i), Key(i) + std::string(100000, 'v'))); // 100K values
+    ASSERT_OK(Put(Key(i), Key(i) + std::string(100000, 'v')));  // 100K values
   }
   Put("foo", "newvalue2");
 
@@ -1205,7 +1331,7 @@ TEST(DBTest, HiddenValuesAreRemoved) {
     Put("pastfoo", "v");
     const Snapshot* snapshot = db_->GetSnapshot();
     Put("foo", "tiny");
-    Put("pastfoo2", "v2");        // Advance sequence number one more
+    Put("pastfoo2", "v2");  // Advance sequence number one more
 
     ASSERT_OK(dbfull()->TEST_CompactMemTable());
     ASSERT_GT(NumTableFilesAtLevel(0), 0);
@@ -1215,11 +1341,11 @@ TEST(DBTest, HiddenValuesAreRemoved) {
     db_->ReleaseSnapshot(snapshot);
     ASSERT_EQ(AllEntriesFor("foo"), "[ tiny, " + big + " ]");
     Slice x("x");
-    dbfull()->TEST_CompactRange(0, NULL, &x);
+    dbfull()->TEST_CompactRange(0, nullptr, &x);
     ASSERT_EQ(AllEntriesFor("foo"), "[ tiny ]");
     ASSERT_EQ(NumTableFilesAtLevel(0), 0);
     ASSERT_GE(NumTableFilesAtLevel(1), 1);
-    dbfull()->TEST_CompactRange(1, NULL, &x);
+    dbfull()->TEST_CompactRange(1, nullptr, &x);
     ASSERT_EQ(AllEntriesFor("foo"), "[ tiny ]");
 
     ASSERT_TRUE(Between(Size("", "pastfoo"), 0, 1000));
@@ -1230,14 +1356,14 @@ TEST(DBTest, DeletionMarkers1) {
   Put("foo", "v1");
   ASSERT_OK(dbfull()->TEST_CompactMemTable());
   const int last = config::kMaxMemCompactLevel;
-  ASSERT_EQ(NumTableFilesAtLevel(last), 1);   // foo => v1 is now in last level
+  ASSERT_EQ(NumTableFilesAtLevel(last), 1);  // foo => v1 is now in last level
 
   // Place a table at level last-1 to prevent merging with preceding mutation
   Put("a", "begin");
   Put("z", "end");
   dbfull()->TEST_CompactMemTable();
   ASSERT_EQ(NumTableFilesAtLevel(last), 1);
-  ASSERT_EQ(NumTableFilesAtLevel(last-1), 1);
+  ASSERT_EQ(NumTableFilesAtLevel(last - 1), 1);
 
   Delete("foo");
   Put("foo", "v2");
@@ -1245,11 +1371,11 @@ TEST(DBTest, DeletionMarkers1) {
   ASSERT_OK(dbfull()->TEST_CompactMemTable());  // Moves to level last-2
   ASSERT_EQ(AllEntriesFor("foo"), "[ v2, DEL, v1 ]");
   Slice z("z");
-  dbfull()->TEST_CompactRange(last-2, NULL, &z);
+  dbfull()->TEST_CompactRange(last - 2, nullptr, &z);
   // DEL eliminated, but v1 remains because we aren't compacting that level
   // (DEL can be eliminated because v2 hides v1).
   ASSERT_EQ(AllEntriesFor("foo"), "[ v2, v1 ]");
-  dbfull()->TEST_CompactRange(last-1, NULL, NULL);
+  dbfull()->TEST_CompactRange(last - 1, nullptr, nullptr);
   // Merging last-1 w/ last, so we are the base level for "foo", so
   // DEL is removed.  (as is v1).
   ASSERT_EQ(AllEntriesFor("foo"), "[ v2 ]");
@@ -1259,23 +1385,23 @@ TEST(DBTest, DeletionMarkers2) {
   Put("foo", "v1");
   ASSERT_OK(dbfull()->TEST_CompactMemTable());
   const int last = config::kMaxMemCompactLevel;
-  ASSERT_EQ(NumTableFilesAtLevel(last), 1);   // foo => v1 is now in last level
+  ASSERT_EQ(NumTableFilesAtLevel(last), 1);  // foo => v1 is now in last level
 
   // Place a table at level last-1 to prevent merging with preceding mutation
   Put("a", "begin");
   Put("z", "end");
   dbfull()->TEST_CompactMemTable();
   ASSERT_EQ(NumTableFilesAtLevel(last), 1);
-  ASSERT_EQ(NumTableFilesAtLevel(last-1), 1);
+  ASSERT_EQ(NumTableFilesAtLevel(last - 1), 1);
 
   Delete("foo");
   ASSERT_EQ(AllEntriesFor("foo"), "[ DEL, v1 ]");
   ASSERT_OK(dbfull()->TEST_CompactMemTable());  // Moves to level last-2
   ASSERT_EQ(AllEntriesFor("foo"), "[ DEL, v1 ]");
-  dbfull()->TEST_CompactRange(last-2, NULL, NULL);
+  dbfull()->TEST_CompactRange(last - 2, nullptr, nullptr);
   // DEL kept: "last" file overlaps
   ASSERT_EQ(AllEntriesFor("foo"), "[ DEL, v1 ]");
-  dbfull()->TEST_CompactRange(last-1, NULL, NULL);
+  dbfull()->TEST_CompactRange(last - 1, nullptr, nullptr);
   // Merging last-1 w/ last, so we are the base level for "foo", so
   // DEL is removed.  (as is v1).
   ASSERT_EQ(AllEntriesFor("foo"), "[ ]");
@@ -1285,7 +1411,8 @@ TEST(DBTest, OverlapInLevel0) {
   do {
     ASSERT_EQ(config::kMaxMemCompactLevel, 2) << "Fix test to match config";
 
-    // Fill levels 1 and 2 to disable the pushing of new memtables to levels > 0.
+    // Fill levels 1 and 2 to disable the pushing of new memtables to levels >
+    // 0.
     ASSERT_OK(Put("100", "v100"));
     ASSERT_OK(Put("999", "v999"));
     dbfull()->TEST_CompactMemTable();
@@ -1308,8 +1435,8 @@ TEST(DBTest, OverlapInLevel0) {
     ASSERT_EQ("2,1,1", FilesPerLevel());
 
     // Compact away the placeholder files we created initially
-    dbfull()->TEST_CompactRange(1, NULL, NULL);
-    dbfull()->TEST_CompactRange(2, NULL, NULL);
+    dbfull()->TEST_CompactRange(1, nullptr, nullptr);
+    dbfull()->TEST_CompactRange(2, nullptr, nullptr);
     ASSERT_EQ("2", FilesPerLevel());
 
     // Do a memtable compaction.  Before bug-fix, the compaction would
@@ -1341,21 +1468,21 @@ TEST(DBTest, L0_CompactionBug_Issue44_a) {
 
 TEST(DBTest, L0_CompactionBug_Issue44_b) {
   Reopen();
-  Put("","");
+  Put("", "");
   Reopen();
   Delete("e");
-  Put("","");
+  Put("", "");
   Reopen();
   Put("c", "cv");
   Reopen();
-  Put("","");
+  Put("", "");
   Reopen();
-  Put("","");
+  Put("", "");
   DelayMilliseconds(1000);  // Wait for compaction to finish
   Reopen();
-  Put("d","dv");
+  Put("d", "dv");
   Reopen();
-  Put("","");
+  Put("", "");
   Reopen();
   Delete("d");
   Delete("b");
@@ -1365,17 +1492,26 @@ TEST(DBTest, L0_CompactionBug_Issue44_b) {
   ASSERT_EQ("(->)(c->cv)", Contents());
 }
 
+TEST(DBTest, Fflush_Issue474) {
+  static const int kNum = 100000;
+  Random rnd(test::RandomSeed());
+  for (int i = 0; i < kNum; i++) {
+    fflush(nullptr);
+    ASSERT_OK(Put(RandomKey(&rnd), RandomString(&rnd, 100)));
+  }
+}
+
 TEST(DBTest, ComparatorCheck) {
   class NewComparator : public Comparator {
    public:
-    virtual const char* Name() const { return "leveldb.NewComparator"; }
-    virtual int Compare(const Slice& a, const Slice& b) const {
+    const char* Name() const override { return "leveldb.NewComparator"; }
+    int Compare(const Slice& a, const Slice& b) const override {
       return BytewiseComparator()->Compare(a, b);
     }
-    virtual void FindShortestSeparator(std::string* s, const Slice& l) const {
+    void FindShortestSeparator(std::string* s, const Slice& l) const override {
       BytewiseComparator()->FindShortestSeparator(s, l);
     }
-    virtual void FindShortSuccessor(std::string* key) const {
+    void FindShortSuccessor(std::string* key) const override {
       BytewiseComparator()->FindShortSuccessor(key);
     }
   };
@@ -1391,21 +1527,22 @@ TEST(DBTest, ComparatorCheck) {
 TEST(DBTest, CustomComparator) {
   class NumberComparator : public Comparator {
    public:
-    virtual const char* Name() const { return "test.NumberComparator"; }
-    virtual int Compare(const Slice& a, const Slice& b) const {
+    const char* Name() const override { return "test.NumberComparator"; }
+    int Compare(const Slice& a, const Slice& b) const override {
       return ToNumber(a) - ToNumber(b);
     }
-    virtual void FindShortestSeparator(std::string* s, const Slice& l) const {
-      ToNumber(*s);     // Check format
-      ToNumber(l);      // Check format
+    void FindShortestSeparator(std::string* s, const Slice& l) const override {
+      ToNumber(*s);  // Check format
+      ToNumber(l);   // Check format
     }
-    virtual void FindShortSuccessor(std::string* key) const {
-      ToNumber(*key);   // Check format
+    void FindShortSuccessor(std::string* key) const override {
+      ToNumber(*key);  // Check format
     }
+
    private:
     static int ToNumber(const Slice& x) {
       // Check that there are no extra characters.
-      ASSERT_TRUE(x.size() >= 2 && x[0] == '[' && x[x.size()-1] == ']')
+      ASSERT_TRUE(x.size() >= 2 && x[0] == '[' && x[x.size() - 1] == ']')
           << EscapeString(x);
       int val;
       char ignored;
@@ -1418,7 +1555,7 @@ TEST(DBTest, CustomComparator) {
   Options new_options = CurrentOptions();
   new_options.create_if_missing = true;
   new_options.comparator = &cmp;
-  new_options.filter_policy = NULL;     // Cannot use bloom filters
+  new_options.filter_policy = nullptr;   // Cannot use bloom filters
   new_options.write_buffer_size = 1000;  // Compact more often
   DestroyAndReopen(&new_options);
   ASSERT_OK(Put("[10]", "ten"));
@@ -1436,7 +1573,7 @@ TEST(DBTest, CustomComparator) {
   for (int run = 0; run < 2; run++) {
     for (int i = 0; i < 1000; i++) {
       char buf[100];
-      snprintf(buf, sizeof(buf), "[%d]", i*10);
+      snprintf(buf, sizeof(buf), "[%d]", i * 10);
       ASSERT_OK(Put(buf, buf));
     }
     Compact("[0]", "[1000000]");
@@ -1473,7 +1610,7 @@ TEST(DBTest, ManualCompaction) {
   // Compact all
   MakeTables(1, "a", "z");
   ASSERT_EQ("0,1,2", FilesPerLevel());
-  db_->CompactRange(NULL, NULL);
+  db_->CompactRange(nullptr, nullptr);
   ASSERT_EQ("0,0,1", FilesPerLevel());
 }
 
@@ -1482,42 +1619,94 @@ TEST(DBTest, DBOpen_Options) {
   DestroyDB(dbname, Options());
 
   // Does not exist, and create_if_missing == false: error
-  DB* db = NULL;
+  DB* db = nullptr;
   Options opts;
   opts.create_if_missing = false;
   Status s = DB::Open(opts, dbname, &db);
-  ASSERT_TRUE(strstr(s.ToString().c_str(), "does not exist") != NULL);
-  ASSERT_TRUE(db == NULL);
+  ASSERT_TRUE(strstr(s.ToString().c_str(), "does not exist") != nullptr);
+  ASSERT_TRUE(db == nullptr);
 
   // Does not exist, and create_if_missing == true: OK
   opts.create_if_missing = true;
   s = DB::Open(opts, dbname, &db);
   ASSERT_OK(s);
-  ASSERT_TRUE(db != NULL);
+  ASSERT_TRUE(db != nullptr);
 
   delete db;
-  db = NULL;
+  db = nullptr;
 
   // Does exist, and error_if_exists == true: error
   opts.create_if_missing = false;
   opts.error_if_exists = true;
   s = DB::Open(opts, dbname, &db);
-  ASSERT_TRUE(strstr(s.ToString().c_str(), "exists") != NULL);
-  ASSERT_TRUE(db == NULL);
+  ASSERT_TRUE(strstr(s.ToString().c_str(), "exists") != nullptr);
+  ASSERT_TRUE(db == nullptr);
 
   // Does exist, and error_if_exists == false: OK
   opts.create_if_missing = true;
   opts.error_if_exists = false;
   s = DB::Open(opts, dbname, &db);
   ASSERT_OK(s);
-  ASSERT_TRUE(db != NULL);
+  ASSERT_TRUE(db != nullptr);
 
   delete db;
-  db = NULL;
+  db = nullptr;
+}
+
+TEST(DBTest, DestroyEmptyDir) {
+  std::string dbname = test::TmpDir() + "/db_empty_dir";
+  TestEnv env(Env::Default());
+  env.DeleteDir(dbname);
+  ASSERT_TRUE(!env.FileExists(dbname));
+
+  Options opts;
+  opts.env = &env;
+
+  ASSERT_OK(env.CreateDir(dbname));
+  ASSERT_TRUE(env.FileExists(dbname));
+  std::vector<std::string> children;
+  ASSERT_OK(env.GetChildren(dbname, &children));
+  // The stock Env's do not filter out '.' and '..' special files.
+  ASSERT_EQ(2, children.size());
+  ASSERT_OK(DestroyDB(dbname, opts));
+  ASSERT_TRUE(!env.FileExists(dbname));
+
+  // Should also be destroyed if Env is filtering out dot files.
+  env.SetIgnoreDotFiles(true);
+  ASSERT_OK(env.CreateDir(dbname));
+  ASSERT_TRUE(env.FileExists(dbname));
+  ASSERT_OK(env.GetChildren(dbname, &children));
+  ASSERT_EQ(0, children.size());
+  ASSERT_OK(DestroyDB(dbname, opts));
+  ASSERT_TRUE(!env.FileExists(dbname));
+}
+
+TEST(DBTest, DestroyOpenDB) {
+  std::string dbname = test::TmpDir() + "/open_db_dir";
+  env_->DeleteDir(dbname);
+  ASSERT_TRUE(!env_->FileExists(dbname));
+
+  Options opts;
+  opts.create_if_missing = true;
+  DB* db = nullptr;
+  ASSERT_OK(DB::Open(opts, dbname, &db));
+  ASSERT_TRUE(db != nullptr);
+
+  // Must fail to destroy an open db.
+  ASSERT_TRUE(env_->FileExists(dbname));
+  ASSERT_TRUE(!DestroyDB(dbname, Options()).ok());
+  ASSERT_TRUE(env_->FileExists(dbname));
+
+  delete db;
+  db = nullptr;
+
+  // Should succeed destroying a closed db.
+  ASSERT_OK(DestroyDB(dbname, Options()));
+  ASSERT_TRUE(!env_->FileExists(dbname));
 }
 
 TEST(DBTest, Locking) {
-  DB* db2 = NULL;
+  DB* db2 = nullptr;
   Status s = DB::Open(CurrentOptions(), dbname_, &db2);
   ASSERT_TRUE(!s.ok()) << "Locking did not prevent re-opening db";
 }
@@ -1532,13 +1721,14 @@ TEST(DBTest, NoSpace) {
   ASSERT_EQ("v1", Get("foo"));
   Compact("a", "z");
   const int num_files = CountFiles();
-  env_->no_space_.Release_Store(env_);   // Force out-of-space errors
+  // Force out-of-space errors.
+  env_->no_space_.store(true, std::memory_order_release);
   for (int i = 0; i < 10; i++) {
-    for (int level = 0; level < config::kNumLevels-1; level++) {
-      dbfull()->TEST_CompactRange(level, NULL, NULL);
+    for (int level = 0; level < config::kNumLevels - 1; level++) {
+      dbfull()->TEST_CompactRange(level, nullptr, nullptr);
     }
   }
-  env_->no_space_.Release_Store(NULL);
+  env_->no_space_.store(false, std::memory_order_release);
   ASSERT_LT(CountFiles(), num_files + 3);
 }
 
@@ -1548,7 +1738,8 @@ TEST(DBTest, NonWritableFileSystem) {
   options.env = env_;
   Reopen(&options);
   ASSERT_OK(Put("foo", "v1"));
-  env_->non_writable_.Release_Store(env_);  // Force errors for new files
+  // Force errors for new files.
+  env_->non_writable_.store(true, std::memory_order_release);
   std::string big(100000, 'x');
   int errors = 0;
   for (int i = 0; i < 20; i++) {
@@ -1559,7 +1750,7 @@ TEST(DBTest, NonWritableFileSystem) {
     }
   }
   ASSERT_GT(errors, 0);
-  env_->non_writable_.Release_Store(NULL);
+  env_->non_writable_.store(false, std::memory_order_release);
 }
 
 TEST(DBTest, WriteSyncError) {
@@ -1569,7 +1760,7 @@ TEST(DBTest, WriteSyncError) {
   Options options = CurrentOptions();
   options.env = env_;
   Reopen(&options);
-  env_->data_sync_error_.Release_Store(env_);
+  env_->data_sync_error_.store(true, std::memory_order_release);
 
   // (b) Normal write should succeed
   WriteOptions w;
@@ -1583,7 +1774,7 @@ TEST(DBTest, WriteSyncError) {
   ASSERT_EQ("NOT_FOUND", Get("k2"));
 
   // (d) make sync behave normally
-  env_->data_sync_error_.Release_Store(NULL);
+  env_->data_sync_error_.store(false, std::memory_order_release);
 
   // (e) Do a non-sync write; should fail
   w.sync = false;
@@ -1603,9 +1794,8 @@ TEST(DBTest, ManifestWriteError) {
   // We iterate twice.  In the second iteration, everything is the
   // same except the log record never makes it to the MANIFEST file.
   for (int iter = 0; iter < 2; iter++) {
-    port::AtomicPointer* error_type = (iter == 0)
-        ? &env_->manifest_sync_error_
-        : &env_->manifest_write_error_;
+    std::atomic<bool>* error_type = (iter == 0) ? &env_->manifest_sync_error_
+                                                : &env_->manifest_write_error_;
 
     // Insert foo=>bar mapping
     Options options = CurrentOptions();
@@ -1620,15 +1810,15 @@ TEST(DBTest, ManifestWriteError) {
     dbfull()->TEST_CompactMemTable();
     ASSERT_EQ("bar", Get("foo"));
     const int last = config::kMaxMemCompactLevel;
-    ASSERT_EQ(NumTableFilesAtLevel(last), 1);   // foo=>bar is now in last level
+    ASSERT_EQ(NumTableFilesAtLevel(last), 1);  // foo=>bar is now in last level
 
     // Merging compaction (will fail)
-    error_type->Release_Store(env_);
-    dbfull()->TEST_CompactRange(last, NULL, NULL);  // Should fail
+    error_type->store(true, std::memory_order_release);
+    dbfull()->TEST_CompactRange(last, nullptr, nullptr);  // Should fail
     ASSERT_EQ("bar", Get("foo"));
 
     // Recovery: should not lose data
-    error_type->Release_Store(NULL);
+    error_type->store(false, std::memory_order_release);
     Reopen(&options);
     ASSERT_EQ("bar", Get("foo"));
   }
@@ -1648,8 +1838,7 @@ TEST(DBTest, MissingSSTFile) {
   options.paranoid_checks = true;
   Status s = TryReopen(&options);
   ASSERT_TRUE(!s.ok());
-  ASSERT_TRUE(s.ToString().find("issing") != std::string::npos)
-      << s.ToString();
+  ASSERT_TRUE(s.ToString().find("issing") != std::string::npos) << s.ToString();
 }
 
 TEST(DBTest, StillReadSST) {
@@ -1699,7 +1888,7 @@ TEST(DBTest, BloomFilter) {
   dbfull()->TEST_CompactMemTable();
 
   // Prevent auto compactions triggered by seeks
-  env_->delay_data_sync_.Release_Store(env_);
+  env_->delay_data_sync_.store(true, std::memory_order_release);
 
   // Lookup present keys.  Should rarely read from small sstable.
   env_->random_read_counter_.Reset();
@@ -1709,7 +1898,7 @@ TEST(DBTest, BloomFilter) {
   int reads = env_->random_read_counter_.Read();
   fprintf(stderr, "%d present => %d reads\n", N, reads);
   ASSERT_GE(reads, N);
-  ASSERT_LE(reads, N + 2*N/100);
+  ASSERT_LE(reads, N + 2 * N / 100);
 
   // Lookup present keys.  Should rarely read from either sstable.
   env_->random_read_counter_.Reset();
@@ -1718,9 +1907,9 @@ TEST(DBTest, BloomFilter) {
   }
   reads = env_->random_read_counter_.Read();
   fprintf(stderr, "%d missing => %d reads\n", N, reads);
-  ASSERT_LE(reads, 3*N/100);
+  ASSERT_LE(reads, 3 * N / 100);
 
-  env_->delay_data_sync_.Release_Store(NULL);
+  env_->delay_data_sync_.store(false, std::memory_order_release);
   Close();
   delete options.block_cache;
   delete options.filter_policy;
@@ -1735,9 +1924,9 @@ static const int kNumKeys = 1000;
 
 struct MTState {
   DBTest* test;
-  port::AtomicPointer stop;
-  port::AtomicPointer counter[kNumThreads];
-  port::AtomicPointer thread_done[kNumThreads];
+  std::atomic<bool> stop;
+  std::atomic<int> counter[kNumThreads];
+  std::atomic<bool> thread_done[kNumThreads];
 };
 
 struct MTThread {
@@ -1749,13 +1938,13 @@ static void MTThreadBody(void* arg) {
   MTThread* t = reinterpret_cast<MTThread*>(arg);
   int id = t->id;
   DB* db = t->state->test->db_;
-  uintptr_t counter = 0;
+  int counter = 0;
   fprintf(stderr, "... starting thread %d\n", id);
   Random rnd(1000 + id);
   std::string value;
   char valbuf[1500];
-  while (t->state->stop.Acquire_Load() == NULL) {
-    t->state->counter[id].Release_Store(reinterpret_cast<void*>(counter));
+  while (!t->state->stop.load(std::memory_order_acquire)) {
+    t->state->counter[id].store(counter, std::memory_order_release);
 
     int key = rnd.Uniform(kNumKeys);
     char keybuf[20];
@@ -1764,8 +1953,8 @@ static void MTThreadBody(void* arg) {
     if (rnd.OneIn(2)) {
       // Write values of the form <key, my id, counter>.
       // We add some padding for force compactions.
-      snprintf(valbuf, sizeof(valbuf), "%d.%d.%-1000d",
-               key, id, static_cast<int>(counter));
+      snprintf(valbuf, sizeof(valbuf), "%d.%d.%-1000d", key, id,
+               static_cast<int>(counter));
       ASSERT_OK(db->Put(WriteOptions(), Slice(keybuf), Slice(valbuf)));
     } else {
       // Read a value and verify that it matches the pattern written above.
@@ -1780,14 +1969,13 @@ static void MTThreadBody(void* arg) {
         ASSERT_EQ(k, key);
         ASSERT_GE(w, 0);
         ASSERT_LT(w, kNumThreads);
-        ASSERT_LE(static_cast<uintptr_t>(c), reinterpret_cast<uintptr_t>(
-            t->state->counter[w].Acquire_Load()));
+        ASSERT_LE(c, t->state->counter[w].load(std::memory_order_acquire));
       }
     }
     counter++;
   }
-  t->state->thread_done[id].Release_Store(t);
-  fprintf(stderr, "... stopping thread %d after %d ops\n", id, int(counter));
+  t->state->thread_done[id].store(true, std::memory_order_release);
+  fprintf(stderr, "... stopping thread %d after %d ops\n", id, counter);
 }
 
 }  // namespace
@@ -1797,10 +1985,10 @@ TEST(DBTest, MultiThreaded) {
     // Initialize state
     MTState mt;
     mt.test = this;
-    mt.stop.Release_Store(0);
+    mt.stop.store(false, std::memory_order_release);
     for (int id = 0; id < kNumThreads; id++) {
-      mt.counter[id].Release_Store(0);
-      mt.thread_done[id].Release_Store(0);
+      mt.counter[id].store(false, std::memory_order_release);
+      mt.thread_done[id].store(false, std::memory_order_release);
     }
 
     // Start threads
@@ -1815,9 +2003,9 @@ TEST(DBTest, MultiThreaded) {
     DelayMilliseconds(kTestSeconds * 1000);
 
     // Stop the threads and wait for them to finish
-    mt.stop.Release_Store(&mt);
+    mt.stop.store(true, std::memory_order_release);
     for (int id = 0; id < kNumThreads; id++) {
-      while (mt.thread_done[id].Acquire_Load() == NULL) {
+      while (!mt.thread_done[id].load(std::memory_order_acquire)) {
         DelayMilliseconds(100);
       }
     }
@@ -1828,28 +2016,28 @@ namespace {
 typedef std::map<std::string, std::string> KVMap;
 }
 
-class ModelDB: public DB {
+class ModelDB : public DB {
  public:
   class ModelSnapshot : public Snapshot {
    public:
     KVMap map_;
   };
 
-  explicit ModelDB(const Options& options): options_(options) { }
-  ~ModelDB() { }
-  virtual Status Put(const WriteOptions& o, const Slice& k, const Slice& v) {
+  explicit ModelDB(const Options& options) : options_(options) {}
+  ~ModelDB() override = default;
+  Status Put(const WriteOptions& o, const Slice& k, const Slice& v) override {
     return DB::Put(o, k, v);
   }
-  virtual Status Delete(const WriteOptions& o, const Slice& key) {
+  Status Delete(const WriteOptions& o, const Slice& key) override {
     return DB::Delete(o, key);
   }
-  virtual Status Get(const ReadOptions& options,
-                     const Slice& key, std::string* value) {
-    assert(false);      // Not implemented
+  Status Get(const ReadOptions& options, const Slice& key,
+             std::string* value) override {
+    assert(false);  // Not implemented
     return Status::NotFound(key);
   }
-  virtual Iterator* NewIterator(const ReadOptions& options) {
-    if (options.snapshot == NULL) {
+  Iterator* NewIterator(const ReadOptions& options) override {
+    if (options.snapshot == nullptr) {
       KVMap* saved = new KVMap;
       *saved = map_;
       return new ModelIter(saved, true);
@@ -1859,68 +2047,65 @@ class ModelDB: public DB {
       return new ModelIter(snapshot_state, false);
     }
   }
-  virtual const Snapshot* GetSnapshot() {
+  const Snapshot* GetSnapshot() override {
     ModelSnapshot* snapshot = new ModelSnapshot;
     snapshot->map_ = map_;
     return snapshot;
   }
 
-  virtual void ReleaseSnapshot(const Snapshot* snapshot) {
+  void ReleaseSnapshot(const Snapshot* snapshot) override {
     delete reinterpret_cast<const ModelSnapshot*>(snapshot);
   }
-  virtual Status Write(const WriteOptions& options, WriteBatch* batch) {
+  Status Write(const WriteOptions& options, WriteBatch* batch) override {
     class Handler : public WriteBatch::Handler {
      public:
       KVMap* map_;
-      virtual void Put(const Slice& key, const Slice& value) {
+      void Put(const Slice& key, const Slice& value) override {
         (*map_)[key.ToString()] = value.ToString();
       }
-      virtual void Delete(const Slice& key) {
-        map_->erase(key.ToString());
-      }
+      void Delete(const Slice& key) override { map_->erase(key.ToString()); }
     };
     Handler handler;
     handler.map_ = &map_;
     return batch->Iterate(&handler);
   }
 
-  virtual bool GetProperty(const Slice& property, std::string* value) {
+  bool GetProperty(const Slice& property, std::string* value) override {
     return false;
   }
-  virtual void GetApproximateSizes(const Range* r, int n, uint64_t* sizes) {
+  void GetApproximateSizes(const Range* r, int n, uint64_t* sizes) override {
     for (int i = 0; i < n; i++) {
       sizes[i] = 0;
     }
   }
-  virtual void CompactRange(const Slice* start, const Slice* end) {
-  }
+  void CompactRange(const Slice* start, const Slice* end) override {}
 
  private:
-  class ModelIter: public Iterator {
+  class ModelIter : public Iterator {
    public:
     ModelIter(const KVMap* map, bool owned)
-        : map_(map), owned_(owned), iter_(map_->end()) {
-    }
-    ~ModelIter() {
+        : map_(map), owned_(owned), iter_(map_->end()) {}
+    ~ModelIter() override {
       if (owned_) delete map_;
     }
-    virtual bool Valid() const { return iter_ != map_->end(); }
-    virtual void SeekToFirst() { iter_ = map_->begin(); }
-    virtual void SeekToLast() {
+    bool Valid() const override { return iter_ != map_->end(); }
+    void SeekToFirst() override { iter_ = map_->begin(); }
+    void SeekToLast() override {
       if (map_->empty()) {
         iter_ = map_->end();
       } else {
         iter_ = map_->find(map_->rbegin()->first);
       }
     }
-    virtual void Seek(const Slice& k) {
+    void Seek(const Slice& k) override {
       iter_ = map_->lower_bound(k.ToString());
     }
-    virtual void Next() { ++iter_; }
-    virtual void Prev() { --iter_; }
-    virtual Slice key() const { return iter_->first; }
-    virtual Slice value() const { return iter_->second; }
-    virtual Status status() const { return Status::OK(); }
+    void Next() override { ++iter_; }
+    void Prev() override { --iter_; }
+    Slice key() const override { return iter_->first; }
+    Slice value() const override { return iter_->second; }
+    Status status() const override { return Status::OK(); }
+
    private:
     const KVMap* const map_;
     const bool owned_;  // Do we own map_
@@ -1930,16 +2115,7 @@ class ModelDB: public DB {
   KVMap map_;
 };
 
-static std::string RandomKey(Random* rnd) {
-  int len = (rnd->OneIn(3)
-             ? 1                // Short sometimes to encourage collisions
-             : (rnd->OneIn(100) ? rnd->Skewed(10) : rnd->Uniform(10)));
-  return test::RandomKey(rnd, len);
-}
-
-static bool CompareIterators(int step,
-                             DB* model,
-                             DB* db,
+static bool CompareIterators(int step, DB* model, DB* db,
                              const Snapshot* model_snap,
                              const Snapshot* db_snap) {
   ReadOptions options;
@@ -1950,12 +2126,10 @@ static bool CompareIterators(int step,
   bool ok = true;
   int count = 0;
   for (miter->SeekToFirst(), dbiter->SeekToFirst();
-       ok && miter->Valid() && dbiter->Valid();
-       miter->Next(), dbiter->Next()) {
+       ok && miter->Valid() && dbiter->Valid(); miter->Next(), dbiter->Next()) {
     count++;
     if (miter->key().compare(dbiter->key()) != 0) {
-      fprintf(stderr, "step %d: Key mismatch: '%s' vs. '%s'\n",
-              step,
+      fprintf(stderr, "step %d: Key mismatch: '%s' vs. '%s'\n", step,
               EscapeString(miter->key()).c_str(),
               EscapeString(dbiter->key()).c_str());
       ok = false;
@@ -1964,8 +2138,7 @@ static bool CompareIterators(int step,
 
     if (miter->value().compare(dbiter->value()) != 0) {
       fprintf(stderr, "step %d: Value mismatch for key '%s': '%s' vs. '%s'\n",
-              step,
-              EscapeString(miter->key()).c_str(),
+              step, EscapeString(miter->key()).c_str(),
               EscapeString(miter->value()).c_str(),
               EscapeString(miter->value()).c_str());
       ok = false;
@@ -1990,8 +2163,8 @@ TEST(DBTest, Randomized) {
   do {
     ModelDB model(CurrentOptions());
     const int N = 10000;
-    const Snapshot* model_snap = NULL;
-    const Snapshot* db_snap = NULL;
+    const Snapshot* model_snap = nullptr;
+    const Snapshot* db_snap = nullptr;
     std::string k, v;
     for (int step = 0; step < N; step++) {
       if (step % 100 == 0) {
@@ -1999,22 +2172,19 @@ TEST(DBTest, Randomized) {
       }
       // TODO(sanjay): Test Get() works
       int p = rnd.Uniform(100);
-      if (p < 45) {                               // Put
+      if (p < 45) {  // Put
         k = RandomKey(&rnd);
-        v = RandomString(&rnd,
-                         rnd.OneIn(20)
-                         ? 100 + rnd.Uniform(100)
-                         : rnd.Uniform(8));
+        v = RandomString(
+            &rnd, rnd.OneIn(20) ? 100 + rnd.Uniform(100) : rnd.Uniform(8));
         ASSERT_OK(model.Put(WriteOptions(), k, v));
         ASSERT_OK(db_->Put(WriteOptions(), k, v));
 
-      } else if (p < 90) {                        // Delete
+      } else if (p < 90) {  // Delete
         k = RandomKey(&rnd);
         ASSERT_OK(model.Delete(WriteOptions(), k));
         ASSERT_OK(db_->Delete(WriteOptions(), k));
 
-
-      } else {                                    // Multi-element batch
+      } else {  // Multi-element batch
         WriteBatch b;
         const int num = rnd.Uniform(8);
         for (int i = 0; i < num; i++) {
@@ -2036,23 +2206,23 @@ TEST(DBTest, Randomized) {
       }
 
       if ((step % 100) == 0) {
-        ASSERT_TRUE(CompareIterators(step, &model, db_, NULL, NULL));
+        ASSERT_TRUE(CompareIterators(step, &model, db_, nullptr, nullptr));
         ASSERT_TRUE(CompareIterators(step, &model, db_, model_snap, db_snap));
         // Save a snapshot from each DB this time that we'll use next
         // time we compare things, to make sure the current state is
         // preserved with the snapshot
-        if (model_snap != NULL) model.ReleaseSnapshot(model_snap);
-        if (db_snap != NULL) db_->ReleaseSnapshot(db_snap);
+        if (model_snap != nullptr) model.ReleaseSnapshot(model_snap);
+        if (db_snap != nullptr) db_->ReleaseSnapshot(db_snap);
 
         Reopen();
-        ASSERT_TRUE(CompareIterators(step, &model, db_, NULL, NULL));
+        ASSERT_TRUE(CompareIterators(step, &model, db_, nullptr, nullptr));
 
         model_snap = model.GetSnapshot();
         db_snap = db_->GetSnapshot();
       }
     }
-    if (model_snap != NULL) model.ReleaseSnapshot(model_snap);
-    if (db_snap != NULL) db_->ReleaseSnapshot(db_snap);
+    if (model_snap != nullptr) model.ReleaseSnapshot(model_snap);
+    if (db_snap != nullptr) db_->ReleaseSnapshot(db_snap);
   } while (ChangeOptions());
 }
 
@@ -2066,15 +2236,15 @@ void BM_LogAndApply(int iters, int num_base_files) {
   std::string dbname = test::TmpDir() + "/leveldb_test_benchmark";
   DestroyDB(dbname, Options());
 
-  DB* db = NULL;
+  DB* db = nullptr;
   Options opts;
   opts.create_if_missing = true;
   Status s = DB::Open(opts, dbname, &db);
   ASSERT_OK(s);
-  ASSERT_TRUE(db != NULL);
+  ASSERT_TRUE(db != nullptr);
 
   delete db;
-  db = NULL;
+  db = nullptr;
 
   Env* env = Env::Default();
 
@@ -2083,13 +2253,14 @@ void BM_LogAndApply(int iters, int num_base_files) {
 
   InternalKeyComparator cmp(BytewiseComparator());
   Options options;
-  VersionSet vset(dbname, &options, NULL, &cmp);
-  ASSERT_OK(vset.Recover());
+  VersionSet vset(dbname, &options, nullptr, &cmp);
+  bool save_manifest;
+  ASSERT_OK(vset.Recover(&save_manifest));
   VersionEdit vbase;
   uint64_t fnum = 1;
   for (int i = 0; i < num_base_files; i++) {
-    InternalKey start(MakeKey(2*fnum), 1, kTypeValue);
-    InternalKey limit(MakeKey(2*fnum+1), 1, kTypeDeletion);
+    InternalKey start(MakeKey(2 * fnum), 1, kTypeValue);
+    InternalKey limit(MakeKey(2 * fnum + 1), 1, kTypeDeletion);
     vbase.AddFile(2, fnum++, 1 /* file size */, start, limit);
   }
   ASSERT_OK(vset.LogAndApply(&vbase, &mu));
@@ -2099,8 +2270,8 @@ void BM_LogAndApply(int iters, int num_base_files) {
   for (int i = 0; i < iters; i++) {
     VersionEdit vedit;
     vedit.DeleteFile(2, fnum);
-    InternalKey start(MakeKey(2*fnum), 1, kTypeValue);
-    InternalKey limit(MakeKey(2*fnum+1), 1, kTypeDeletion);
+    InternalKey start(MakeKey(2 * fnum), 1, kTypeValue);
+    InternalKey limit(MakeKey(2 * fnum + 1), 1, kTypeDeletion);
     vedit.AddFile(2, fnum++, 1 /* file size */, start, limit);
     vset.LogAndApply(&vedit, &mu);
   }
@@ -2109,8 +2280,8 @@ void BM_LogAndApply(int iters, int num_base_files) {
   char buf[16];
   snprintf(buf, sizeof(buf), "%d", num_base_files);
   fprintf(stderr,
-          "BM_LogAndApply/%-6s   %8d iters : %9u us (%7.0f us / iter)\n",
-          buf, iters, us, ((float)us) / iters);
+          "BM_LogAndApply/%-6s   %8d iters : %9u us (%7.0f us / iter)\n", buf,
+          iters, us, ((float)us) / iters);
 }
 
 }  // namespace leveldb
diff --git a/db/dbformat.cc b/db/dbformat.cc
index 20a7ca4..459eddf 100644
--- a/db/dbformat.cc
+++ b/db/dbformat.cc
@@ -2,8 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
-#include <stdio.h>
 #include "db/dbformat.h"
+
+#include <stdio.h>
+
+#include <sstream>
+
 #include "port/port.h"
 #include "util/coding.h"
 
@@ -21,26 +25,20 @@ void AppendInternalKey(std::string* result, const ParsedInternalKey& key) {
 }
 
 std::string ParsedInternalKey::DebugString() const {
-  char buf[50];
-  snprintf(buf, sizeof(buf), "' @ %llu : %d",
-           (unsigned long long) sequence,
-           int(type));
-  std::string result = "'";
-  result += EscapeString(user_key.ToString());
-  result += buf;
-  return result;
+  std::ostringstream ss;
+  ss << '\'' << EscapeString(user_key.ToString()) << "' @ " << sequence << " : "
+     << static_cast<int>(type);
+  return ss.str();
 }
 
 std::string InternalKey::DebugString() const {
-  std::string result;
   ParsedInternalKey parsed;
   if (ParseInternalKey(rep_, &parsed)) {
-    result = parsed.DebugString();
-  } else {
-    result = "(bad)";
-    result.append(EscapeString(rep_));
+    return parsed.DebugString();
   }
-  return result;
+  std::ostringstream ss;
+  ss << "(bad)" << EscapeString(rep_);
+  return ss.str();
 }
 
 const char* InternalKeyComparator::Name() const {
@@ -65,9 +63,8 @@ int InternalKeyComparator::Compare(const Slice& akey, const Slice& bkey) const {
   return r;
 }
 
-void InternalKeyComparator::FindShortestSeparator(
-      std::string* start,
-      const Slice& limit) const {
+void InternalKeyComparator::FindShortestSeparator(std::string* start,
+                                                  const Slice& limit) const {
   // Attempt to shorten the user portion of the key
   Slice user_start = ExtractUserKey(*start);
   Slice user_limit = ExtractUserKey(limit);
@@ -77,7 +74,8 @@ void InternalKeyComparator::FindShortestSeparator(
       user_comparator_->Compare(user_start, tmp) < 0) {
     // User key has become shorter physically, but larger logically.
     // Tack on the earliest possible number to the shortened user key.
-    PutFixed64(&tmp, PackSequenceAndType(kMaxSequenceNumber,kValueTypeForSeek));
+    PutFixed64(&tmp,
+               PackSequenceAndType(kMaxSequenceNumber, kValueTypeForSeek));
     assert(this->Compare(*start, tmp) < 0);
     assert(this->Compare(tmp, limit) < 0);
     start->swap(tmp);
@@ -92,15 +90,14 @@ void InternalKeyComparator::FindShortSuccessor(std::string* key) const {
       user_comparator_->Compare(user_key, tmp) < 0) {
     // User key has become shorter physically, but larger logically.
     // Tack on the earliest possible number to the shortened user key.
-    PutFixed64(&tmp, PackSequenceAndType(kMaxSequenceNumber,kValueTypeForSeek));
+    PutFixed64(&tmp,
+               PackSequenceAndType(kMaxSequenceNumber, kValueTypeForSeek));
     assert(this->Compare(*key, tmp) < 0);
     key->swap(tmp);
   }
 }
 
-const char* InternalFilterPolicy::Name() const {
-  return user_policy_->Name();
-}
+const char* InternalFilterPolicy::Name() const { return user_policy_->Name(); }
 
 void InternalFilterPolicy::CreateFilter(const Slice* keys, int n,
                                         std::string* dst) const {
diff --git a/db/dbformat.h b/db/dbformat.h
index ea897b1..abcb489 100644
--- a/db/dbformat.h
+++ b/db/dbformat.h
@@ -6,6 +6,7 @@
 #define STORAGE_LEVELDB_DB_DBFORMAT_H_
 
 #include <stdio.h>
+
 #include "leveldb/comparator.h"
 #include "leveldb/db.h"
 #include "leveldb/filter_policy.h"
@@ -48,10 +49,7 @@ class InternalKey;
 // Value types encoded as the last component of internal keys.
 // DO NOT CHANGE THESE ENUM VALUES: they are embedded in the on-disk
 // data structures.
-enum ValueType {
-  kTypeDeletion = 0x0,
-  kTypeValue = 0x1
-};
+enum ValueType { kTypeDeletion = 0x0, kTypeValue = 0x1 };
 // kValueTypeForSeek defines the ValueType that should be passed when
 // constructing a ParsedInternalKey object for seeking to a particular
 // sequence number (since we sort sequence numbers in decreasing order
@@ -64,17 +62,16 @@ typedef uint64_t SequenceNumber;
 
 // We leave eight bits empty at the bottom so a type and sequence#
 // can be packed together into 64-bits.
-static const SequenceNumber kMaxSequenceNumber =
-    ((0x1ull << 56) - 1);
+static const SequenceNumber kMaxSequenceNumber = ((0x1ull << 56) - 1);
 
 struct ParsedInternalKey {
   Slice user_key;
   SequenceNumber sequence;
   ValueType type;
 
-  ParsedInternalKey() { }  // Intentionally left uninitialized (for speed)
+  ParsedInternalKey() {}  // Intentionally left uninitialized (for speed)
   ParsedInternalKey(const Slice& u, const SequenceNumber& seq, ValueType t)
-      : user_key(u), sequence(seq), type(t) { }
+      : user_key(u), sequence(seq), type(t) {}
   std::string DebugString() const;
 };
 
@@ -84,15 +81,13 @@ inline size_t InternalKeyEncodingLength(const ParsedInternalKey& key) {
 }
 
 // Append the serialization of "key" to *result.
-extern void AppendInternalKey(std::string* result,
-                              const ParsedInternalKey& key);
+void AppendInternalKey(std::string* result, const ParsedInternalKey& key);
 
 // Attempt to parse an internal key from "internal_key".  On success,
 // stores the parsed data in "*result", and returns true.
 //
 // On error, returns false, leaves "*result" in an undefined state.
-extern bool ParseInternalKey(const Slice& internal_key,
-                             ParsedInternalKey* result);
+bool ParseInternalKey(const Slice& internal_key, ParsedInternalKey* result);
 
 // Returns the user key portion of an internal key.
 inline Slice ExtractUserKey(const Slice& internal_key) {
@@ -100,27 +95,19 @@ inline Slice ExtractUserKey(const Slice& internal_key) {
   return Slice(internal_key.data(), internal_key.size() - 8);
 }
 
-inline ValueType ExtractValueType(const Slice& internal_key) {
-  assert(internal_key.size() >= 8);
-  const size_t n = internal_key.size();
-  uint64_t num = DecodeFixed64(internal_key.data() + n - 8);
-  unsigned char c = num & 0xff;
-  return static_cast<ValueType>(c);
-}
-
 // A comparator for internal keys that uses a specified comparator for
 // the user key portion and breaks ties by decreasing sequence number.
 class InternalKeyComparator : public Comparator {
  private:
   const Comparator* user_comparator_;
+
  public:
-  explicit InternalKeyComparator(const Comparator* c) : user_comparator_(c) { }
-  virtual const char* Name() const;
-  virtual int Compare(const Slice& a, const Slice& b) const;
-  virtual void FindShortestSeparator(
-      std::string* start,
-      const Slice& limit) const;
-  virtual void FindShortSuccessor(std::string* key) const;
+  explicit InternalKeyComparator(const Comparator* c) : user_comparator_(c) {}
+  const char* Name() const override;
+  int Compare(const Slice& a, const Slice& b) const override;
+  void FindShortestSeparator(std::string* start,
+                             const Slice& limit) const override;
+  void FindShortSuccessor(std::string* key) const override;
 
   const Comparator* user_comparator() const { return user_comparator_; }
 
@@ -131,11 +118,12 @@ class InternalKeyComparator : public Comparator {
 class InternalFilterPolicy : public FilterPolicy {
  private:
   const FilterPolicy* const user_policy_;
+
  public:
-  explicit InternalFilterPolicy(const FilterPolicy* p) : user_policy_(p) { }
-  virtual const char* Name() const;
-  virtual void CreateFilter(const Slice* keys, int n, std::string* dst) const;
-  virtual bool KeyMayMatch(const Slice& key, const Slice& filter) const;
+  explicit InternalFilterPolicy(const FilterPolicy* p) : user_policy_(p) {}
+  const char* Name() const override;
+  void CreateFilter(const Slice* keys, int n, std::string* dst) const override;
+  bool KeyMayMatch(const Slice& key, const Slice& filter) const override;
 };
 
 // Modules in this directory should keep internal keys wrapped inside
@@ -144,13 +132,18 @@ class InternalFilterPolicy : public FilterPolicy {
 class InternalKey {
  private:
   std::string rep_;
+
  public:
-  InternalKey() { }   // Leave rep_ as empty to indicate it is invalid
+  InternalKey() {}  // Leave rep_ as empty to indicate it is invalid
   InternalKey(const Slice& user_key, SequenceNumber s, ValueType t) {
     AppendInternalKey(&rep_, ParsedInternalKey(user_key, s, t));
   }
 
-  void DecodeFrom(const Slice& s) { rep_.assign(s.data(), s.size()); }
+  bool DecodeFrom(const Slice& s) {
+    rep_.assign(s.data(), s.size());
+    return !rep_.empty();
+  }
+
   Slice Encode() const {
     assert(!rep_.empty());
     return rep_;
@@ -168,8 +161,8 @@ class InternalKey {
   std::string DebugString() const;
 };
 
-inline int InternalKeyComparator::Compare(
-    const InternalKey& a, const InternalKey& b) const {
+inline int InternalKeyComparator::Compare(const InternalKey& a,
+                                          const InternalKey& b) const {
   return Compare(a.Encode(), b.Encode());
 }
 
@@ -192,6 +185,9 @@ class LookupKey {
   // the specified sequence number.
   LookupKey(const Slice& user_key, SequenceNumber sequence);
 
+  LookupKey(const LookupKey&) = delete;
+  LookupKey& operator=(const LookupKey&) = delete;
+
   ~LookupKey();
 
   // Return a key suitable for lookup in a MemTable.
@@ -214,11 +210,7 @@ class LookupKey {
   const char* start_;
   const char* kstart_;
   const char* end_;
-  char space_[200];      // Avoid allocation for short keys
-
-  // No copying allowed
-  LookupKey(const LookupKey&);
-  void operator=(const LookupKey&);
+  char space_[200];  // Avoid allocation for short keys
 };
 
 inline LookupKey::~LookupKey() {
diff --git a/db/dbformat_test.cc b/db/dbformat_test.cc
index 5d82f5d..1209369 100644
--- a/db/dbformat_test.cc
+++ b/db/dbformat_test.cc
@@ -8,8 +8,7 @@
 
 namespace leveldb {
 
-static std::string IKey(const std::string& user_key,
-                        uint64_t seq,
+static std::string IKey(const std::string& user_key, uint64_t seq,
                         ValueType vt) {
   std::string encoded;
   AppendInternalKey(&encoded, ParsedInternalKey(user_key, seq, vt));
@@ -28,9 +27,7 @@ static std::string ShortSuccessor(const std::string& s) {
   return result;
 }
 
-static void TestKey(const std::string& key,
-                    uint64_t seq,
-                    ValueType vt) {
+static void TestKey(const std::string& key, uint64_t seq, ValueType vt) {
   std::string encoded = IKey(key, seq, vt);
 
   Slice in(encoded);
@@ -44,16 +41,22 @@ static void TestKey(const std::string& key,
   ASSERT_TRUE(!ParseInternalKey(Slice("bar"), &decoded));
 }
 
-class FormatTest { };
+class FormatTest {};
 
 TEST(FormatTest, InternalKey_EncodeDecode) {
-  const char* keys[] = { "", "k", "hello", "longggggggggggggggggggggg" };
-  const uint64_t seq[] = {
-    1, 2, 3,
-    (1ull << 8) - 1, 1ull << 8, (1ull << 8) + 1,
-    (1ull << 16) - 1, 1ull << 16, (1ull << 16) + 1,
-    (1ull << 32) - 1, 1ull << 32, (1ull << 32) + 1
-  };
+  const char* keys[] = {"", "k", "hello", "longggggggggggggggggggggg"};
+  const uint64_t seq[] = {1,
+                          2,
+                          3,
+                          (1ull << 8) - 1,
+                          1ull << 8,
+                          (1ull << 8) + 1,
+                          (1ull << 16) - 1,
+                          1ull << 16,
+                          (1ull << 16) + 1,
+                          (1ull << 32) - 1,
+                          1ull << 32,
+                          (1ull << 32) + 1};
   for (int k = 0; k < sizeof(keys) / sizeof(keys[0]); k++) {
     for (int s = 0; s < sizeof(seq) / sizeof(seq[0]); s++) {
       TestKey(keys[k], seq[s], kTypeValue);
@@ -62,40 +65,44 @@ TEST(FormatTest, InternalKey_EncodeDecode) {
   }
 }
 
+TEST(FormatTest, InternalKey_DecodeFromEmpty) {
+  InternalKey internal_key;
+
+  ASSERT_TRUE(!internal_key.DecodeFrom(""));
+}
+
 TEST(FormatTest, InternalKeyShortSeparator) {
   // When user keys are same
   ASSERT_EQ(IKey("foo", 100, kTypeValue),
-            Shorten(IKey("foo", 100, kTypeValue),
-                    IKey("foo", 99, kTypeValue)));
-  ASSERT_EQ(IKey("foo", 100, kTypeValue),
-            Shorten(IKey("foo", 100, kTypeValue),
-                    IKey("foo", 101, kTypeValue)));
-  ASSERT_EQ(IKey("foo", 100, kTypeValue),
-            Shorten(IKey("foo", 100, kTypeValue),
-                    IKey("foo", 100, kTypeValue)));
-  ASSERT_EQ(IKey("foo", 100, kTypeValue),
-            Shorten(IKey("foo", 100, kTypeValue),
-                    IKey("foo", 100, kTypeDeletion)));
+            Shorten(IKey("foo", 100, kTypeValue), IKey("foo", 99, kTypeValue)));
+  ASSERT_EQ(
+      IKey("foo", 100, kTypeValue),
+      Shorten(IKey("foo", 100, kTypeValue), IKey("foo", 101, kTypeValue)));
+  ASSERT_EQ(
+      IKey("foo", 100, kTypeValue),
+      Shorten(IKey("foo", 100, kTypeValue), IKey("foo", 100, kTypeValue)));
+  ASSERT_EQ(
+      IKey("foo", 100, kTypeValue),
+      Shorten(IKey("foo", 100, kTypeValue), IKey("foo", 100, kTypeDeletion)));
 
   // When user keys are misordered
   ASSERT_EQ(IKey("foo", 100, kTypeValue),
-            Shorten(IKey("foo", 100, kTypeValue),
-                    IKey("bar", 99, kTypeValue)));
+            Shorten(IKey("foo", 100, kTypeValue), IKey("bar", 99, kTypeValue)));
 
   // When user keys are different, but correctly ordered
-  ASSERT_EQ(IKey("g", kMaxSequenceNumber, kValueTypeForSeek),
-            Shorten(IKey("foo", 100, kTypeValue),
-                    IKey("hello", 200, kTypeValue)));
+  ASSERT_EQ(
+      IKey("g", kMaxSequenceNumber, kValueTypeForSeek),
+      Shorten(IKey("foo", 100, kTypeValue), IKey("hello", 200, kTypeValue)));
 
   // When start user key is prefix of limit user key
-  ASSERT_EQ(IKey("foo", 100, kTypeValue),
-            Shorten(IKey("foo", 100, kTypeValue),
-                    IKey("foobar", 200, kTypeValue)));
+  ASSERT_EQ(
+      IKey("foo", 100, kTypeValue),
+      Shorten(IKey("foo", 100, kTypeValue), IKey("foobar", 200, kTypeValue)));
 
   // When limit user key is prefix of start user key
-  ASSERT_EQ(IKey("foobar", 100, kTypeValue),
-            Shorten(IKey("foobar", 100, kTypeValue),
-                    IKey("foo", 200, kTypeValue)));
+  ASSERT_EQ(
+      IKey("foobar", 100, kTypeValue),
+      Shorten(IKey("foobar", 100, kTypeValue), IKey("foo", 200, kTypeValue)));
 }
 
 TEST(FormatTest, InternalKeyShortestSuccessor) {
@@ -105,8 +112,20 @@ TEST(FormatTest, InternalKeyShortestSuccessor) {
             ShortSuccessor(IKey("\xff\xff", 100, kTypeValue)));
 }
 
-}  // namespace leveldb
+TEST(FormatTest, ParsedInternalKeyDebugString) {
+  ParsedInternalKey key("The \"key\" in 'single quotes'", 42, kTypeValue);
+
+  ASSERT_EQ("'The \"key\" in 'single quotes'' @ 42 : 1", key.DebugString());
+}
+
+TEST(FormatTest, InternalKeyDebugString) {
+  InternalKey key("The \"key\" in 'single quotes'", 42, kTypeValue);
+  ASSERT_EQ("'The \"key\" in 'single quotes'' @ 42 : 1", key.DebugString());
 
-int main(int argc, char** argv) {
-  return leveldb::test::RunAllTests();
+  InternalKey invalid_key;
+  ASSERT_EQ("(bad)", invalid_key.DebugString());
 }
+
+}  // namespace leveldb
+
+int main(int argc, char** argv) { return leveldb::test::RunAllTests(); }
diff --git a/db/dumpfile.cc b/db/dumpfile.cc
index 61c47c2..77d5900 100644
--- a/db/dumpfile.cc
+++ b/db/dumpfile.cc
@@ -2,7 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
+#include "leveldb/dumpfile.h"
+
 #include <stdio.h>
+
 #include "db/dbformat.h"
 #include "db/filename.h"
 #include "db/log_reader.h"
@@ -35,8 +38,7 @@ bool GuessType(const std::string& fname, FileType* type) {
 // Notified when log reader encounters corruption.
 class CorruptionReporter : public log::Reader::Reporter {
  public:
-  WritableFile* dst_;
-  virtual void Corruption(size_t bytes, const Status& status) {
+  void Corruption(size_t bytes, const Status& status) override {
     std::string r = "corruption: ";
     AppendNumberTo(&r, bytes);
     r += " bytes; ";
@@ -44,6 +46,8 @@ class CorruptionReporter : public log::Reader::Reporter {
     r.push_back('\n');
     dst_->Append(r);
   }
+
+  WritableFile* dst_;
 };
 
 // Print contents of a log file. (*func)() is called on every record.
@@ -70,8 +74,7 @@ Status PrintLogContents(Env* env, const std::string& fname,
 // Called on every item found in a WriteBatch.
 class WriteBatchItemPrinter : public WriteBatch::Handler {
  public:
-  WritableFile* dst_;
-  virtual void Put(const Slice& key, const Slice& value) {
+  void Put(const Slice& key, const Slice& value) override {
     std::string r = "  put '";
     AppendEscapedStringTo(&r, key);
     r += "' '";
@@ -79,14 +82,15 @@ class WriteBatchItemPrinter : public WriteBatch::Handler {
     r += "'\n";
     dst_->Append(r);
   }
-  virtual void Delete(const Slice& key) {
+  void Delete(const Slice& key) override {
     std::string r = "  del '";
     AppendEscapedStringTo(&r, key);
     r += "'\n";
     dst_->Append(r);
   }
-};
 
+  WritableFile* dst_;
+};
 
 // Called on every log record (each one of which is a WriteBatch)
 // found in a kLogFile.
@@ -142,8 +146,8 @@ Status DumpDescriptor(Env* env, const std::string& fname, WritableFile* dst) {
 
 Status DumpTable(Env* env, const std::string& fname, WritableFile* dst) {
   uint64_t file_size;
-  RandomAccessFile* file = NULL;
-  Table* table = NULL;
+  RandomAccessFile* file = nullptr;
+  Table* table = nullptr;
   Status s = env->GetFileSize(fname, &file_size);
   if (s.ok()) {
     s = env->NewRandomAccessFile(fname, &file);
@@ -213,9 +217,12 @@ Status DumpFile(Env* env, const std::string& fname, WritableFile* dst) {
     return Status::InvalidArgument(fname + ": unknown file type");
   }
   switch (ftype) {
-    case kLogFile:         return DumpLog(env, fname, dst);
-    case kDescriptorFile:  return DumpDescriptor(env, fname, dst);
-    case kTableFile:       return DumpTable(env, fname, dst);
+    case kLogFile:
+      return DumpLog(env, fname, dst);
+    case kDescriptorFile:
+      return DumpDescriptor(env, fname, dst);
+    case kTableFile:
+      return DumpTable(env, fname, dst);
     default:
       break;
   }
diff --git a/db/fault_injection_test.cc b/db/fault_injection_test.cc
index 8e3e603..5b31bb8 100644
--- a/db/fault_injection_test.cc
+++ b/db/fault_injection_test.cc
@@ -6,18 +6,20 @@
 // the last "sync". It then checks for data loss errors by purposely dropping
 // file data (or entire files) not protected by a "sync".
 
-#include "leveldb/db.h"
-
 #include <map>
 #include <set>
+
 #include "db/db_impl.h"
 #include "db/filename.h"
 #include "db/log_format.h"
 #include "db/version_set.h"
 #include "leveldb/cache.h"
+#include "leveldb/db.h"
 #include "leveldb/env.h"
 #include "leveldb/table.h"
 #include "leveldb/write_batch.h"
+#include "port/port.h"
+#include "port/thread_annotations.h"
 #include "util/logging.h"
 #include "util/mutexlock.h"
 #include "util/testharness.h"
@@ -34,7 +36,7 @@ class FaultInjectionTestEnv;
 namespace {
 
 // Assume a filename, and not a directory name like "/foo/bar/"
-static std::string GetDirName(const std::string filename) {
+static std::string GetDirName(const std::string& filename) {
   size_t found = filename.find_last_of("/\\");
   if (found == std::string::npos) {
     return "";
@@ -54,8 +56,7 @@ Status Truncate(const std::string& filename, uint64_t length) {
 
   SequentialFile* orig_file;
   Status s = env->NewSequentialFile(filename, &orig_file);
-  if (!s.ok())
-    return s;
+  if (!s.ok()) return s;
 
   char* scratch = new char[length];
   leveldb::Slice result;
@@ -83,15 +84,15 @@ Status Truncate(const std::string& filename, uint64_t length) {
 
 struct FileState {
   std::string filename_;
-  ssize_t pos_;
-  ssize_t pos_at_last_sync_;
-  ssize_t pos_at_last_flush_;
+  int64_t pos_;
+  int64_t pos_at_last_sync_;
+  int64_t pos_at_last_flush_;
 
   FileState(const std::string& filename)
       : filename_(filename),
         pos_(-1),
         pos_at_last_sync_(-1),
-        pos_at_last_flush_(-1) { }
+        pos_at_last_flush_(-1) {}
 
   FileState() : pos_(-1), pos_at_last_sync_(-1), pos_at_last_flush_(-1) {}
 
@@ -106,14 +107,13 @@ struct FileState {
 // is written to or sync'ed.
 class TestWritableFile : public WritableFile {
  public:
-  TestWritableFile(const std::string& fname,
-                   WritableFile* f,
+  TestWritableFile(const FileState& state, WritableFile* f,
                    FaultInjectionTestEnv* env);
-  virtual ~TestWritableFile();
-  virtual Status Append(const Slice& data);
-  virtual Status Close();
-  virtual Status Flush();
-  virtual Status Sync();
+  ~TestWritableFile() override;
+  Status Append(const Slice& data) override;
+  Status Close() override;
+  Status Flush() override;
+  Status Sync() override;
 
  private:
   FileState state_;
@@ -126,12 +126,15 @@ class TestWritableFile : public WritableFile {
 
 class FaultInjectionTestEnv : public EnvWrapper {
  public:
-  FaultInjectionTestEnv() : EnvWrapper(Env::Default()), filesystem_active_(true) {}
-  virtual ~FaultInjectionTestEnv() { }
-  virtual Status NewWritableFile(const std::string& fname,
-                                 WritableFile** result);
-  virtual Status DeleteFile(const std::string& f);
-  virtual Status RenameFile(const std::string& s, const std::string& t);
+  FaultInjectionTestEnv()
+      : EnvWrapper(Env::Default()), filesystem_active_(true) {}
+  ~FaultInjectionTestEnv() override = default;
+  Status NewWritableFile(const std::string& fname,
+                         WritableFile** result) override;
+  Status NewAppendableFile(const std::string& fname,
+                           WritableFile** result) override;
+  Status DeleteFile(const std::string& f) override;
+  Status RenameFile(const std::string& s, const std::string& t) override;
 
   void WritableFileClosed(const FileState& state);
   Status DropUnsyncedFileData();
@@ -144,25 +147,26 @@ class FaultInjectionTestEnv : public EnvWrapper {
   // system reset. Setting to inactive will freeze our saved filesystem state so
   // that it will stop being recorded. It can then be reset back to the state at
   // the time of the reset.
-  bool IsFilesystemActive() const { return filesystem_active_; }
-  void SetFilesystemActive(bool active) { filesystem_active_ = active; }
+  bool IsFilesystemActive() LOCKS_EXCLUDED(mutex_) {
+    MutexLock l(&mutex_);
+    return filesystem_active_;
+  }
+  void SetFilesystemActive(bool active) LOCKS_EXCLUDED(mutex_) {
+    MutexLock l(&mutex_);
+    filesystem_active_ = active;
+  }
 
  private:
   port::Mutex mutex_;
-  std::map<std::string, FileState> db_file_state_;
-  std::set<std::string> new_files_since_last_dir_sync_;
-  bool filesystem_active_;  // Record flushes, syncs, writes
+  std::map<std::string, FileState> db_file_state_ GUARDED_BY(mutex_);
+  std::set<std::string> new_files_since_last_dir_sync_ GUARDED_BY(mutex_);
+  bool filesystem_active_ GUARDED_BY(mutex_);  // Record flushes, syncs, writes
 };
 
-TestWritableFile::TestWritableFile(const std::string& fname,
-                                   WritableFile* f,
+TestWritableFile::TestWritableFile(const FileState& state, WritableFile* f,
                                    FaultInjectionTestEnv* env)
-    : state_(fname),
-      target_(f),
-      writable_file_opened_(true),
-      env_(env) {
-  assert(f != NULL);
-  state_.pos_ = 0;
+    : state_(state), target_(f), writable_file_opened_(true), env_(env) {
+  assert(f != nullptr);
 }
 
 TestWritableFile::~TestWritableFile() {
@@ -228,9 +232,12 @@ Status FaultInjectionTestEnv::NewWritableFile(const std::string& fname,
   WritableFile* actual_writable_file;
   Status s = target()->NewWritableFile(fname, &actual_writable_file);
   if (s.ok()) {
-    *result = new TestWritableFile(fname, actual_writable_file, this);
-    // WritableFile doesn't append to files, so if the same file is opened again
-    // then it will be truncated - so forget our saved state.
+    FileState state(fname);
+    state.pos_ = 0;
+    *result = new TestWritableFile(state, actual_writable_file, this);
+    // NewWritableFile doesn't append to files, so if the same file is
+    // opened again then it will be truncated - so forget our saved
+    // state.
     UntrackFile(fname);
     MutexLock l(&mutex_);
     new_files_since_last_dir_sync_.insert(fname);
@@ -238,13 +245,34 @@ Status FaultInjectionTestEnv::NewWritableFile(const std::string& fname,
   return s;
 }
 
+Status FaultInjectionTestEnv::NewAppendableFile(const std::string& fname,
+                                                WritableFile** result) {
+  WritableFile* actual_writable_file;
+  Status s = target()->NewAppendableFile(fname, &actual_writable_file);
+  if (s.ok()) {
+    FileState state(fname);
+    state.pos_ = 0;
+    {
+      MutexLock l(&mutex_);
+      if (db_file_state_.count(fname) == 0) {
+        new_files_since_last_dir_sync_.insert(fname);
+      } else {
+        state = db_file_state_[fname];
+      }
+    }
+    *result = new TestWritableFile(state, actual_writable_file, this);
+  }
+  return s;
+}
+
 Status FaultInjectionTestEnv::DropUnsyncedFileData() {
   Status s;
   MutexLock l(&mutex_);
-  for (std::map<std::string, FileState>::const_iterator it =
-           db_file_state_.begin();
-       s.ok() && it != db_file_state_.end(); ++it) {
-    const FileState& state = it->second;
+  for (const auto& kvp : db_file_state_) {
+    if (!s.ok()) {
+      break;
+    }
+    const FileState& state = kvp.second;
     if (!state.IsFullySynced()) {
       s = state.DropUnsyncedData();
     }
@@ -301,9 +329,9 @@ Status FaultInjectionTestEnv::RenameFile(const std::string& s,
 }
 
 void FaultInjectionTestEnv::ResetState() {
-  MutexLock l(&mutex_);
-  db_file_state_.clear();
-  new_files_since_last_dir_sync_.clear();
+  // Since we are not destroying the database, the existing files
+  // should keep their recorded synced/flushed state. Therefore
+  // we do not reset db_file_state_ and new_files_since_last_dir_sync_.
   SetFilesystemActive(true);
 }
 
@@ -313,12 +341,14 @@ Status FaultInjectionTestEnv::DeleteFilesCreatedAfterLastDirSync() {
   std::set<std::string> new_files(new_files_since_last_dir_sync_.begin(),
                                   new_files_since_last_dir_sync_.end());
   mutex_.Unlock();
-  Status s;
-  std::set<std::string>::const_iterator it;
-  for (it = new_files.begin(); s.ok() && it != new_files.end(); ++it) {
-    s = DeleteFile(*it);
+  Status status;
+  for (const auto& new_file : new_files) {
+    Status delete_status = DeleteFile(new_file);
+    if (!delete_status.ok() && status.ok()) {
+      status = std::move(delete_status);
+    }
   }
-  return s;
+  return status;
 }
 
 void FaultInjectionTestEnv::WritableFileClosed(const FileState& state) {
@@ -327,7 +357,7 @@ void FaultInjectionTestEnv::WritableFileClosed(const FileState& state) {
 }
 
 Status FileState::DropUnsyncedData() const {
-  ssize_t sync_pos = pos_at_last_sync_ == -1 ? 0 : pos_at_last_sync_;
+  int64_t sync_pos = pos_at_last_sync_ == -1 ? 0 : pos_at_last_sync_;
   return Truncate(filename_, sync_pos);
 }
 
@@ -342,53 +372,28 @@ class FaultInjectionTest {
   Options options_;
   DB* db_;
 
-  FaultInjectionTest() : env_(NULL), tiny_cache_(NULL), db_(NULL) { NewDB(); }
-
-  ~FaultInjectionTest() { ASSERT_OK(TearDown()); }
-
-  Status NewDB() {
-    assert(db_ == NULL);
-    assert(tiny_cache_ == NULL);
-    assert(env_ == NULL);
-
-    env_ = new FaultInjectionTestEnv();
-
-    options_ = Options();
+  FaultInjectionTest()
+      : env_(new FaultInjectionTestEnv),
+        tiny_cache_(NewLRUCache(100)),
+        db_(nullptr) {
+    dbname_ = test::TmpDir() + "/fault_test";
+    DestroyDB(dbname_, Options());  // Destroy any db from earlier run
+    options_.reuse_logs = true;
     options_.env = env_;
     options_.paranoid_checks = true;
-
-    tiny_cache_ = NewLRUCache(100);
     options_.block_cache = tiny_cache_;
-    dbname_ = test::TmpDir() + "/fault_test";
-
     options_.create_if_missing = true;
-    Status s = OpenDB();
-    options_.create_if_missing = false;
-    return s;
   }
 
-  Status SetUp() {
-    Status s = TearDown();
-    if (s.ok()) {
-      s = NewDB();
-    }
-    return s;
-  }
-
-  Status TearDown() {
+  ~FaultInjectionTest() {
     CloseDB();
-
-    Status s = DestroyDB(dbname_, Options());
-
+    DestroyDB(dbname_, Options());
     delete tiny_cache_;
-    tiny_cache_ = NULL;
-
     delete env_;
-    env_ = NULL;
-
-    return s;
   }
 
+  void ReuseLogs(bool reuse) { options_.reuse_logs = reuse; }
+
   void Build(int start_idx, int num_vals) {
     std::string key_space, value_space;
     WriteBatch batch;
@@ -447,19 +452,18 @@ class FaultInjectionTest {
 
   Status OpenDB() {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
     env_->ResetState();
     return DB::Open(options_, dbname_, &db_);
   }
 
   void CloseDB() {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
   }
 
   void DeleteAllData() {
     Iterator* iter = db_->NewIterator(ReadOptions());
-    WriteOptions options;
     for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
       ASSERT_OK(db_->Delete(WriteOptions(), iter->key()));
     }
@@ -483,60 +487,65 @@ class FaultInjectionTest {
   void PartialCompactTestPreFault(int num_pre_sync, int num_post_sync) {
     DeleteAllData();
     Build(0, num_pre_sync);
-    db_->CompactRange(NULL, NULL);
+    db_->CompactRange(nullptr, nullptr);
     Build(num_pre_sync, num_post_sync);
   }
 
   void PartialCompactTestReopenWithFault(ResetMethod reset_method,
-                                         int num_pre_sync,
-                                         int num_post_sync) {
+                                         int num_pre_sync, int num_post_sync) {
     env_->SetFilesystemActive(false);
     CloseDB();
     ResetDBState(reset_method);
     ASSERT_OK(OpenDB());
     ASSERT_OK(Verify(0, num_pre_sync, FaultInjectionTest::VAL_EXPECT_NO_ERROR));
-    ASSERT_OK(Verify(num_pre_sync, num_post_sync, FaultInjectionTest::VAL_EXPECT_ERROR));
+    ASSERT_OK(Verify(num_pre_sync, num_post_sync,
+                     FaultInjectionTest::VAL_EXPECT_ERROR));
   }
 
-  void NoWriteTestPreFault() {
-  }
+  void NoWriteTestPreFault() {}
 
   void NoWriteTestReopenWithFault(ResetMethod reset_method) {
     CloseDB();
     ResetDBState(reset_method);
     ASSERT_OK(OpenDB());
   }
-};
 
-TEST(FaultInjectionTest, FaultTest) {
-  Random rnd(0);
-  ASSERT_OK(SetUp());
-  for (size_t idx = 0; idx < kNumIterations; idx++) {
-    int num_pre_sync = rnd.Uniform(kMaxNumValues);
-    int num_post_sync = rnd.Uniform(kMaxNumValues);
+  void DoTest() {
+    Random rnd(0);
+    ASSERT_OK(OpenDB());
+    for (size_t idx = 0; idx < kNumIterations; idx++) {
+      int num_pre_sync = rnd.Uniform(kMaxNumValues);
+      int num_post_sync = rnd.Uniform(kMaxNumValues);
 
-    PartialCompactTestPreFault(num_pre_sync, num_post_sync);
-    PartialCompactTestReopenWithFault(RESET_DROP_UNSYNCED_DATA,
-                                      num_pre_sync,
-                                      num_post_sync);
+      PartialCompactTestPreFault(num_pre_sync, num_post_sync);
+      PartialCompactTestReopenWithFault(RESET_DROP_UNSYNCED_DATA, num_pre_sync,
+                                        num_post_sync);
 
-    NoWriteTestPreFault();
-    NoWriteTestReopenWithFault(RESET_DROP_UNSYNCED_DATA);
+      NoWriteTestPreFault();
+      NoWriteTestReopenWithFault(RESET_DROP_UNSYNCED_DATA);
 
-    PartialCompactTestPreFault(num_pre_sync, num_post_sync);
-    // No new files created so we expect all values since no files will be
-    // dropped.
-    PartialCompactTestReopenWithFault(RESET_DELETE_UNSYNCED_FILES,
-                                      num_pre_sync + num_post_sync,
-                                      0);
+      PartialCompactTestPreFault(num_pre_sync, num_post_sync);
+      // No new files created so we expect all values since no files will be
+      // dropped.
+      PartialCompactTestReopenWithFault(RESET_DELETE_UNSYNCED_FILES,
+                                        num_pre_sync + num_post_sync, 0);
 
-    NoWriteTestPreFault();
-    NoWriteTestReopenWithFault(RESET_DELETE_UNSYNCED_FILES);
+      NoWriteTestPreFault();
+      NoWriteTestReopenWithFault(RESET_DELETE_UNSYNCED_FILES);
+    }
   }
+};
+
+TEST(FaultInjectionTest, FaultTestNoLogReuse) {
+  ReuseLogs(false);
+  DoTest();
+}
+
+TEST(FaultInjectionTest, FaultTestWithLogReuse) {
+  ReuseLogs(true);
+  DoTest();
 }
 
 }  // namespace leveldb
 
-int main(int argc, char** argv) {
-  return leveldb::test::RunAllTests();
-}
+int main(int argc, char** argv) { return leveldb::test::RunAllTests(); }
diff --git a/db/filename.cc b/db/filename.cc
index da32946..85de45c 100644
--- a/db/filename.cc
+++ b/db/filename.cc
@@ -2,9 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
+#include "db/filename.h"
+
 #include <ctype.h>
 #include <stdio.h>
-#include "db/filename.h"
+
 #include "db/dbformat.h"
 #include "leveldb/env.h"
 #include "util/logging.h"
@@ -12,31 +14,30 @@
 namespace leveldb {
 
 // A utility routine: write "data" to the named file and Sync() it.
-extern Status WriteStringToFileSync(Env* env, const Slice& data,
-                                    const std::string& fname);
+Status WriteStringToFileSync(Env* env, const Slice& data,
+                             const std::string& fname);
 
-static std::string MakeFileName(const std::string& name, uint64_t number,
+static std::string MakeFileName(const std::string& dbname, uint64_t number,
                                 const char* suffix) {
   char buf[100];
   snprintf(buf, sizeof(buf), "/%06llu.%s",
-           static_cast<unsigned long long>(number),
-           suffix);
-  return name + buf;
+           static_cast<unsigned long long>(number), suffix);
+  return dbname + buf;
 }
 
-std::string LogFileName(const std::string& name, uint64_t number) {
+std::string LogFileName(const std::string& dbname, uint64_t number) {
   assert(number > 0);
-  return MakeFileName(name, number, "log");
+  return MakeFileName(dbname, number, "log");
 }
 
-std::string TableFileName(const std::string& name, uint64_t number) {
+std::string TableFileName(const std::string& dbname, uint64_t number) {
   assert(number > 0);
-  return MakeFileName(name, number, "ldb");
+  return MakeFileName(dbname, number, "ldb");
 }
 
-std::string SSTTableFileName(const std::string& name, uint64_t number) {
+std::string SSTTableFileName(const std::string& dbname, uint64_t number) {
   assert(number > 0);
-  return MakeFileName(name, number, "sst");
+  return MakeFileName(dbname, number, "sst");
 }
 
 std::string DescriptorFileName(const std::string& dbname, uint64_t number) {
@@ -51,9 +52,7 @@ std::string CurrentFileName(const std::string& dbname) {
   return dbname + "/CURRENT";
 }
 
-std::string LockFileName(const std::string& dbname) {
-  return dbname + "/LOCK";
-}
+std::string LockFileName(const std::string& dbname) { return dbname + "/LOCK"; }
 
 std::string TempFileName(const std::string& dbname, uint64_t number) {
   assert(number > 0);
@@ -69,7 +68,6 @@ std::string OldInfoLogFileName(const std::string& dbname) {
   return dbname + "/LOG.old";
 }
 
-
 // Owned filenames have the form:
 //    dbname/CURRENT
 //    dbname/LOCK
@@ -77,10 +75,9 @@ std::string OldInfoLogFileName(const std::string& dbname) {
 //    dbname/LOG.old
 //    dbname/MANIFEST-[0-9]+
 //    dbname/[0-9]+.(log|sst|ldb)
-bool ParseFileName(const std::string& fname,
-                   uint64_t* number,
+bool ParseFileName(const std::string& filename, uint64_t* number,
                    FileType* type) {
-  Slice rest(fname);
+  Slice rest(filename);
   if (rest == "CURRENT") {
     *number = 0;
     *type = kCurrentFile;
diff --git a/db/filename.h b/db/filename.h
index 87a7526..524e813 100644
--- a/db/filename.h
+++ b/db/filename.h
@@ -8,7 +8,9 @@
 #define STORAGE_LEVELDB_DB_FILENAME_H_
 
 #include <stdint.h>
+
 #include <string>
+
 #include "leveldb/slice.h"
 #include "leveldb/status.h"
 #include "port/port.h"
@@ -30,55 +32,52 @@ enum FileType {
 // Return the name of the log file with the specified number
 // in the db named by "dbname".  The result will be prefixed with
 // "dbname".
-extern std::string LogFileName(const std::string& dbname, uint64_t number);
+std::string LogFileName(const std::string& dbname, uint64_t number);
 
 // Return the name of the sstable with the specified number
 // in the db named by "dbname".  The result will be prefixed with
 // "dbname".
-extern std::string TableFileName(const std::string& dbname, uint64_t number);
+std::string TableFileName(const std::string& dbname, uint64_t number);
 
 // Return the legacy file name for an sstable with the specified number
 // in the db named by "dbname". The result will be prefixed with
 // "dbname".
-extern std::string SSTTableFileName(const std::string& dbname, uint64_t number);
+std::string SSTTableFileName(const std::string& dbname, uint64_t number);
 
 // Return the name of the descriptor file for the db named by
 // "dbname" and the specified incarnation number.  The result will be
 // prefixed with "dbname".
-extern std::string DescriptorFileName(const std::string& dbname,
-                                      uint64_t number);
+std::string DescriptorFileName(const std::string& dbname, uint64_t number);
 
 // Return the name of the current file.  This file contains the name
 // of the current manifest file.  The result will be prefixed with
 // "dbname".
-extern std::string CurrentFileName(const std::string& dbname);
+std::string CurrentFileName(const std::string& dbname);
 
 // Return the name of the lock file for the db named by
 // "dbname".  The result will be prefixed with "dbname".
-extern std::string LockFileName(const std::string& dbname);
+std::string LockFileName(const std::string& dbname);
 
 // Return the name of a temporary file owned by the db named "dbname".
 // The result will be prefixed with "dbname".
-extern std::string TempFileName(const std::string& dbname, uint64_t number);
+std::string TempFileName(const std::string& dbname, uint64_t number);
 
 // Return the name of the info log file for "dbname".
-extern std::string InfoLogFileName(const std::string& dbname);
+std::string InfoLogFileName(const std::string& dbname);
 
 // Return the name of the old info log file for "dbname".
-extern std::string OldInfoLogFileName(const std::string& dbname);
+std::string OldInfoLogFileName(const std::string& dbname);
 
 // If filename is a leveldb file, store the type of the file in *type.
 // The number encoded in the filename is stored in *number.  If the
 // filename was successfully parsed, returns true.  Else return false.
-extern bool ParseFileName(const std::string& filename,
-                          uint64_t* number,
-                          FileType* type);
+bool ParseFileName(const std::string& filename, uint64_t* number,
+                   FileType* type);
 
 // Make the CURRENT file point to the descriptor file with the
 // specified number.
-extern Status SetCurrentFile(Env* env, const std::string& dbname,
-                             uint64_t descriptor_number);
-
+Status SetCurrentFile(Env* env, const std::string& dbname,
+                      uint64_t descriptor_number);
 
 }  // namespace leveldb
 
diff --git a/db/filename_test.cc b/db/filename_test.cc
index a32556d..952f320 100644
--- a/db/filename_test.cc
+++ b/db/filename_test.cc
@@ -11,7 +11,7 @@
 
 namespace leveldb {
 
-class FileNameTest { };
+class FileNameTest {};
 
 TEST(FileNameTest, Parse) {
   Slice db;
@@ -24,17 +24,17 @@ TEST(FileNameTest, Parse) {
     uint64_t number;
     FileType type;
   } cases[] = {
-    { "100.log",            100,   kLogFile },
-    { "0.log",              0,     kLogFile },
-    { "0.sst",              0,     kTableFile },
-    { "0.ldb",              0,     kTableFile },
-    { "CURRENT",            0,     kCurrentFile },
-    { "LOCK",               0,     kDBLockFile },
-    { "MANIFEST-2",         2,     kDescriptorFile },
-    { "MANIFEST-7",         7,     kDescriptorFile },
-    { "LOG",                0,     kInfoLogFile },
-    { "LOG.old",            0,     kInfoLogFile },
-    { "18446744073709551615.log", 18446744073709551615ull, kLogFile },
+      {"100.log", 100, kLogFile},
+      {"0.log", 0, kLogFile},
+      {"0.sst", 0, kTableFile},
+      {"0.ldb", 0, kTableFile},
+      {"CURRENT", 0, kCurrentFile},
+      {"LOCK", 0, kDBLockFile},
+      {"MANIFEST-2", 2, kDescriptorFile},
+      {"MANIFEST-7", 7, kDescriptorFile},
+      {"LOG", 0, kInfoLogFile},
+      {"LOG.old", 0, kInfoLogFile},
+      {"18446744073709551615.log", 18446744073709551615ull, kLogFile},
   };
   for (int i = 0; i < sizeof(cases) / sizeof(cases[0]); i++) {
     std::string f = cases[i].fname;
@@ -44,30 +44,28 @@ TEST(FileNameTest, Parse) {
   }
 
   // Errors
-  static const char* errors[] = {
-    "",
-    "foo",
-    "foo-dx-100.log",
-    ".log",
-    "",
-    "manifest",
-    "CURREN",
-    "CURRENTX",
-    "MANIFES",
-    "MANIFEST",
-    "MANIFEST-",
-    "XMANIFEST-3",
-    "MANIFEST-3x",
-    "LOC",
-    "LOCKx",
-    "LO",
-    "LOGx",
-    "18446744073709551616.log",
-    "184467440737095516150.log",
-    "100",
-    "100.",
-    "100.lop"
-  };
+  static const char* errors[] = {"",
+                                 "foo",
+                                 "foo-dx-100.log",
+                                 ".log",
+                                 "",
+                                 "manifest",
+                                 "CURREN",
+                                 "CURRENTX",
+                                 "MANIFES",
+                                 "MANIFEST",
+                                 "MANIFEST-",
+                                 "XMANIFEST-3",
+                                 "MANIFEST-3x",
+                                 "LOC",
+                                 "LOCKx",
+                                 "LO",
+                                 "LOGx",
+                                 "18446744073709551616.log",
+                                 "184467440737095516150.log",
+                                 "100",
+                                 "100.",
+                                 "100.lop"};
   for (int i = 0; i < sizeof(errors) / sizeof(errors[0]); i++) {
     std::string f = errors[i];
     ASSERT_TRUE(!ParseFileName(f, &number, &type)) << f;
@@ -114,10 +112,20 @@ TEST(FileNameTest, Construction) {
   ASSERT_TRUE(ParseFileName(fname.c_str() + 4, &number, &type));
   ASSERT_EQ(999, number);
   ASSERT_EQ(kTempFile, type);
+
+  fname = InfoLogFileName("foo");
+  ASSERT_EQ("foo/", std::string(fname.data(), 4));
+  ASSERT_TRUE(ParseFileName(fname.c_str() + 4, &number, &type));
+  ASSERT_EQ(0, number);
+  ASSERT_EQ(kInfoLogFile, type);
+
+  fname = OldInfoLogFileName("foo");
+  ASSERT_EQ("foo/", std::string(fname.data(), 4));
+  ASSERT_TRUE(ParseFileName(fname.c_str() + 4, &number, &type));
+  ASSERT_EQ(0, number);
+  ASSERT_EQ(kInfoLogFile, type);
 }
 
 }  // namespace leveldb
 
-int main(int argc, char** argv) {
-  return leveldb::test::RunAllTests();
-}
+int main(int argc, char** argv) { return leveldb::test::RunAllTests(); }
diff --git a/db/leveldb_main.cc b/db/leveldbutil.cc
index 9f4b7dd..55cdcc5 100644
--- a/db/leveldb_main.cc
+++ b/db/leveldbutil.cc
@@ -3,6 +3,7 @@
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
 #include <stdio.h>
+
 #include "leveldb/dumpfile.h"
 #include "leveldb/env.h"
 #include "leveldb/status.h"
@@ -12,13 +13,13 @@ namespace {
 
 class StdoutPrinter : public WritableFile {
  public:
-  virtual Status Append(const Slice& data) {
+  Status Append(const Slice& data) override {
     fwrite(data.data(), 1, data.size(), stdout);
     return Status::OK();
   }
-  virtual Status Close() { return Status::OK(); }
-  virtual Status Flush() { return Status::OK(); }
-  virtual Status Sync() { return Status::OK(); }
+  Status Close() override { return Status::OK(); }
+  Status Flush() override { return Status::OK(); }
+  Status Sync() override { return Status::OK(); }
 };
 
 bool HandleDumpCommand(Env* env, char** files, int num) {
@@ -38,11 +39,9 @@ bool HandleDumpCommand(Env* env, char** files, int num) {
 }  // namespace leveldb
 
 static void Usage() {
-  fprintf(
-      stderr,
-      "Usage: leveldbutil command...\n"
-      "   dump files...         -- dump contents of specified files\n"
-      );
+  fprintf(stderr,
+          "Usage: leveldbutil command...\n"
+          "   dump files...         -- dump contents of specified files\n");
 }
 
 int main(int argc, char** argv) {
@@ -54,7 +53,7 @@ int main(int argc, char** argv) {
   } else {
     std::string command = argv[1];
     if (command == "dump") {
-      ok = leveldb::HandleDumpCommand(env, argv+2, argc-2);
+      ok = leveldb::HandleDumpCommand(env, argv + 2, argc - 2);
     } else {
       Usage();
       ok = false;
diff --git a/db/log_format.h b/db/log_format.h
index a8c06ef..356e69f 100644
--- a/db/log_format.h
+++ b/db/log_format.h
@@ -3,7 +3,7 @@
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 //
 // Log format information shared by reader and writer.
-// See ../doc/log_format.txt for more detail.
+// See ../doc/log_format.md for more detail.
 
 #ifndef STORAGE_LEVELDB_DB_LOG_FORMAT_H_
 #define STORAGE_LEVELDB_DB_LOG_FORMAT_H_
diff --git a/db/log_reader.cc b/db/log_reader.cc
index e44b66c..b770fee 100644
--- a/db/log_reader.cc
+++ b/db/log_reader.cc
@@ -5,6 +5,7 @@
 #include "db/log_reader.h"
 
 #include <stdio.h>
+
 #include "leveldb/env.h"
 #include "util/coding.h"
 #include "util/crc32c.h"
@@ -12,8 +13,7 @@
 namespace leveldb {
 namespace log {
 
-Reader::Reporter::~Reporter() {
-}
+Reader::Reporter::~Reporter() = default;
 
 Reader::Reader(SequentialFile* file, Reporter* reporter, bool checksum,
                uint64_t initial_offset)
@@ -25,20 +25,17 @@ Reader::Reader(SequentialFile* file, Reporter* reporter, bool checksum,
       eof_(false),
       last_record_offset_(0),
       end_of_buffer_offset_(0),
-      initial_offset_(initial_offset) {
-}
+      initial_offset_(initial_offset),
+      resyncing_(initial_offset > 0) {}
 
-Reader::~Reader() {
-  delete[] backing_store_;
-}
+Reader::~Reader() { delete[] backing_store_; }
 
 bool Reader::SkipToInitialBlock() {
-  size_t offset_in_block = initial_offset_ % kBlockSize;
+  const size_t offset_in_block = initial_offset_ % kBlockSize;
   uint64_t block_start_location = initial_offset_ - offset_in_block;
 
   // Don't search a block if we'd be in the trailer
   if (offset_in_block > kBlockSize - 6) {
-    offset_in_block = 0;
     block_start_location += kBlockSize;
   }
 
@@ -72,8 +69,25 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch) {
 
   Slice fragment;
   while (true) {
-    uint64_t physical_record_offset = end_of_buffer_offset_ - buffer_.size();
     const unsigned int record_type = ReadPhysicalRecord(&fragment);
+
+    // ReadPhysicalRecord may have only had an empty trailer remaining in its
+    // internal buffer. Calculate the offset of the next physical record now
+    // that it has returned, properly accounting for its header size.
+    uint64_t physical_record_offset =
+        end_of_buffer_offset_ - buffer_.size() - kHeaderSize - fragment.size();
+
+    if (resyncing_) {
+      if (record_type == kMiddleType) {
+        continue;
+      } else if (record_type == kLastType) {
+        resyncing_ = false;
+        continue;
+      } else {
+        resyncing_ = false;
+      }
+    }
+
     switch (record_type) {
       case kFullType:
         if (in_fragmented_record) {
@@ -81,9 +95,7 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch) {
           // it could emit an empty kFirstType record at the tail end
           // of a block followed by a kFullType or kFirstType record
           // at the beginning of the next block.
-          if (scratch->empty()) {
-            in_fragmented_record = false;
-          } else {
+          if (!scratch->empty()) {
             ReportCorruption(scratch->size(), "partial record without end(1)");
           }
         }
@@ -99,9 +111,7 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch) {
           // it could emit an empty kFirstType record at the tail end
           // of a block followed by a kFullType or kFirstType record
           // at the beginning of the next block.
-          if (scratch->empty()) {
-            in_fragmented_record = false;
-          } else {
+          if (!scratch->empty()) {
             ReportCorruption(scratch->size(), "partial record without end(2)");
           }
         }
@@ -163,16 +173,14 @@ bool Reader::ReadRecord(Slice* record, std::string* scratch) {
   return false;
 }
 
-uint64_t Reader::LastRecordOffset() {
-  return last_record_offset_;
-}
+uint64_t Reader::LastRecordOffset() { return last_record_offset_; }
 
 void Reader::ReportCorruption(uint64_t bytes, const char* reason) {
   ReportDrop(bytes, Status::Corruption(reason));
 }
 
 void Reader::ReportDrop(uint64_t bytes, const Status& reason) {
-  if (reporter_ != NULL &&
+  if (reporter_ != nullptr &&
       end_of_buffer_offset_ - buffer_.size() - bytes >= initial_offset_) {
     reporter_->Corruption(static_cast<size_t>(bytes), reason);
   }
diff --git a/db/log_reader.h b/db/log_reader.h
index 6aff791..001da89 100644
--- a/db/log_reader.h
+++ b/db/log_reader.h
@@ -32,7 +32,7 @@ class Reader {
   // Create a reader that will return log records from "*file".
   // "*file" must remain live while this Reader is in use.
   //
-  // If "reporter" is non-NULL, it is notified whenever some data is
+  // If "reporter" is non-null, it is notified whenever some data is
   // dropped due to a detected corruption.  "*reporter" must remain
   // live while this Reader is in use.
   //
@@ -43,6 +43,9 @@ class Reader {
   Reader(SequentialFile* file, Reporter* reporter, bool checksum,
          uint64_t initial_offset);
 
+  Reader(const Reader&) = delete;
+  Reader& operator=(const Reader&) = delete;
+
   ~Reader();
 
   // Read the next record into *record.  Returns true if read
@@ -58,21 +61,6 @@ class Reader {
   uint64_t LastRecordOffset();
 
  private:
-  SequentialFile* const file_;
-  Reporter* const reporter_;
-  bool const checksum_;
-  char* const backing_store_;
-  Slice buffer_;
-  bool eof_;   // Last Read() indicated EOF by returning < kBlockSize
-
-  // Offset of the last record returned by ReadRecord.
-  uint64_t last_record_offset_;
-  // Offset of the first location past the end of buffer_.
-  uint64_t end_of_buffer_offset_;
-
-  // Offset at which to start looking for the first record to return
-  uint64_t const initial_offset_;
-
   // Extend record types with the following special values
   enum {
     kEof = kMaxRecordType + 1,
@@ -97,9 +85,25 @@ class Reader {
   void ReportCorruption(uint64_t bytes, const char* reason);
   void ReportDrop(uint64_t bytes, const Status& reason);
 
-  // No copying allowed
-  Reader(const Reader&);
-  void operator=(const Reader&);
+  SequentialFile* const file_;
+  Reporter* const reporter_;
+  bool const checksum_;
+  char* const backing_store_;
+  Slice buffer_;
+  bool eof_;  // Last Read() indicated EOF by returning < kBlockSize
+
+  // Offset of the last record returned by ReadRecord.
+  uint64_t last_record_offset_;
+  // Offset of the first location past the end of buffer_.
+  uint64_t end_of_buffer_offset_;
+
+  // Offset at which to start looking for the first record to return
+  uint64_t const initial_offset_;
+
+  // True if we are resynchronizing after a seek (initial_offset_ > 0). In
+  // particular, a run of kMiddleType and kLastType records can be silently
+  // skipped in this mode
+  bool resyncing_;
 };
 
 }  // namespace log
diff --git a/db/log_test.cc b/db/log_test.cc
index dcf0562..0e31648 100644
--- a/db/log_test.cc
+++ b/db/log_test.cc
@@ -37,95 +37,29 @@ static std::string RandomSkewedString(int i, Random* rnd) {
 }
 
 class LogTest {
- private:
-  class StringDest : public WritableFile {
-   public:
-    std::string contents_;
-
-    virtual Status Close() { return Status::OK(); }
-    virtual Status Flush() { return Status::OK(); }
-    virtual Status Sync() { return Status::OK(); }
-    virtual Status Append(const Slice& slice) {
-      contents_.append(slice.data(), slice.size());
-      return Status::OK();
-    }
-  };
-
-  class StringSource : public SequentialFile {
-   public:
-    Slice contents_;
-    bool force_error_;
-    bool returned_partial_;
-    StringSource() : force_error_(false), returned_partial_(false) { }
-
-    virtual Status Read(size_t n, Slice* result, char* scratch) {
-      ASSERT_TRUE(!returned_partial_) << "must not Read() after eof/error";
-
-      if (force_error_) {
-        force_error_ = false;
-        returned_partial_ = true;
-        return Status::Corruption("read error");
-      }
-
-      if (contents_.size() < n) {
-        n = contents_.size();
-        returned_partial_ = true;
-      }
-      *result = Slice(contents_.data(), n);
-      contents_.remove_prefix(n);
-      return Status::OK();
-    }
-
-    virtual Status Skip(uint64_t n) {
-      if (n > contents_.size()) {
-        contents_.clear();
-        return Status::NotFound("in-memory file skipepd past end");
-      }
-
-      contents_.remove_prefix(n);
-
-      return Status::OK();
-    }
-  };
-
-  class ReportCollector : public Reader::Reporter {
-   public:
-    size_t dropped_bytes_;
-    std::string message_;
-
-    ReportCollector() : dropped_bytes_(0) { }
-    virtual void Corruption(size_t bytes, const Status& status) {
-      dropped_bytes_ += bytes;
-      message_.append(status.ToString());
-    }
-  };
-
-  StringDest dest_;
-  StringSource source_;
-  ReportCollector report_;
-  bool reading_;
-  Writer writer_;
-  Reader reader_;
-
-  // Record metadata for testing initial offset functionality
-  static size_t initial_offset_record_sizes_[];
-  static uint64_t initial_offset_last_record_offsets_[];
-
  public:
-  LogTest() : reading_(false),
-              writer_(&dest_),
-              reader_(&source_, &report_, true/*checksum*/,
-                      0/*initial_offset*/) {
+  LogTest()
+      : reading_(false),
+        writer_(new Writer(&dest_)),
+        reader_(new Reader(&source_, &report_, true /*checksum*/,
+                           0 /*initial_offset*/)) {}
+
+  ~LogTest() {
+    delete writer_;
+    delete reader_;
+  }
+
+  void ReopenForAppend() {
+    delete writer_;
+    writer_ = new Writer(&dest_, dest_.contents_.size());
   }
 
   void Write(const std::string& msg) {
     ASSERT_TRUE(!reading_) << "Write() after starting to read";
-    writer_.AddRecord(Slice(msg));
+    writer_->AddRecord(Slice(msg));
   }
 
-  size_t WrittenBytes() const {
-    return dest_.contents_.size();
-  }
+  size_t WrittenBytes() const { return dest_.contents_.size(); }
 
   std::string Read() {
     if (!reading_) {
@@ -134,7 +68,7 @@ class LogTest {
     }
     std::string scratch;
     Slice record;
-    if (reader_.ReadRecord(&record, &scratch)) {
+    if (reader_->ReadRecord(&record, &scratch)) {
       return record.ToString();
     } else {
       return "EOF";
@@ -155,22 +89,16 @@ class LogTest {
 
   void FixChecksum(int header_offset, int len) {
     // Compute crc of type/len/data
-    uint32_t crc = crc32c::Value(&dest_.contents_[header_offset+6], 1 + len);
+    uint32_t crc = crc32c::Value(&dest_.contents_[header_offset + 6], 1 + len);
     crc = crc32c::Mask(crc);
     EncodeFixed32(&dest_.contents_[header_offset], crc);
   }
 
-  void ForceError() {
-    source_.force_error_ = true;
-  }
+  void ForceError() { source_.force_error_ = true; }
 
-  size_t DroppedBytes() const {
-    return report_.dropped_bytes_;
-  }
+  size_t DroppedBytes() const { return report_.dropped_bytes_; }
 
-  std::string ReportMessage() const {
-    return report_.message_;
-  }
+  std::string ReportMessage() const { return report_.message_; }
 
   // Returns OK iff recorded error message contains "msg"
   std::string MatchError(const std::string& msg) const {
@@ -182,18 +110,23 @@ class LogTest {
   }
 
   void WriteInitialOffsetLog() {
-    for (int i = 0; i < 4; i++) {
+    for (int i = 0; i < num_initial_offset_records_; i++) {
       std::string record(initial_offset_record_sizes_[i],
                          static_cast<char>('a' + i));
       Write(record);
     }
   }
 
+  void StartReadingAt(uint64_t initial_offset) {
+    delete reader_;
+    reader_ = new Reader(&source_, &report_, true /*checksum*/, initial_offset);
+  }
+
   void CheckOffsetPastEndReturnsNoRecords(uint64_t offset_past_end) {
     WriteInitialOffsetLog();
     reading_ = true;
     source_.contents_ = Slice(dest_.contents_);
-    Reader* offset_reader = new Reader(&source_, &report_, true/*checksum*/,
+    Reader* offset_reader = new Reader(&source_, &report_, true /*checksum*/,
                                        WrittenBytes() + offset_past_end);
     Slice record;
     std::string scratch;
@@ -206,38 +139,126 @@ class LogTest {
     WriteInitialOffsetLog();
     reading_ = true;
     source_.contents_ = Slice(dest_.contents_);
-    Reader* offset_reader = new Reader(&source_, &report_, true/*checksum*/,
-                                       initial_offset);
-    Slice record;
-    std::string scratch;
-    ASSERT_TRUE(offset_reader->ReadRecord(&record, &scratch));
-    ASSERT_EQ(initial_offset_record_sizes_[expected_record_offset],
-              record.size());
-    ASSERT_EQ(initial_offset_last_record_offsets_[expected_record_offset],
-              offset_reader->LastRecordOffset());
-    ASSERT_EQ((char)('a' + expected_record_offset), record.data()[0]);
+    Reader* offset_reader =
+        new Reader(&source_, &report_, true /*checksum*/, initial_offset);
+
+    // Read all records from expected_record_offset through the last one.
+    ASSERT_LT(expected_record_offset, num_initial_offset_records_);
+    for (; expected_record_offset < num_initial_offset_records_;
+         ++expected_record_offset) {
+      Slice record;
+      std::string scratch;
+      ASSERT_TRUE(offset_reader->ReadRecord(&record, &scratch));
+      ASSERT_EQ(initial_offset_record_sizes_[expected_record_offset],
+                record.size());
+      ASSERT_EQ(initial_offset_last_record_offsets_[expected_record_offset],
+                offset_reader->LastRecordOffset());
+      ASSERT_EQ((char)('a' + expected_record_offset), record.data()[0]);
+    }
     delete offset_reader;
   }
 
+ private:
+  class StringDest : public WritableFile {
+   public:
+    Status Close() override { return Status::OK(); }
+    Status Flush() override { return Status::OK(); }
+    Status Sync() override { return Status::OK(); }
+    Status Append(const Slice& slice) override {
+      contents_.append(slice.data(), slice.size());
+      return Status::OK();
+    }
+
+    std::string contents_;
+  };
+
+  class StringSource : public SequentialFile {
+   public:
+    StringSource() : force_error_(false), returned_partial_(false) {}
+
+    Status Read(size_t n, Slice* result, char* scratch) override {
+      ASSERT_TRUE(!returned_partial_) << "must not Read() after eof/error";
+
+      if (force_error_) {
+        force_error_ = false;
+        returned_partial_ = true;
+        return Status::Corruption("read error");
+      }
+
+      if (contents_.size() < n) {
+        n = contents_.size();
+        returned_partial_ = true;
+      }
+      *result = Slice(contents_.data(), n);
+      contents_.remove_prefix(n);
+      return Status::OK();
+    }
+
+    Status Skip(uint64_t n) override {
+      if (n > contents_.size()) {
+        contents_.clear();
+        return Status::NotFound("in-memory file skipped past end");
+      }
+
+      contents_.remove_prefix(n);
+
+      return Status::OK();
+    }
+
+    Slice contents_;
+    bool force_error_;
+    bool returned_partial_;
+  };
+
+  class ReportCollector : public Reader::Reporter {
+   public:
+    ReportCollector() : dropped_bytes_(0) {}
+    void Corruption(size_t bytes, const Status& status) override {
+      dropped_bytes_ += bytes;
+      message_.append(status.ToString());
+    }
+
+    size_t dropped_bytes_;
+    std::string message_;
+  };
+
+  // Record metadata for testing initial offset functionality
+  static size_t initial_offset_record_sizes_[];
+  static uint64_t initial_offset_last_record_offsets_[];
+  static int num_initial_offset_records_;
+
+  StringDest dest_;
+  StringSource source_;
+  ReportCollector report_;
+  bool reading_;
+  Writer* writer_;
+  Reader* reader_;
 };
 
-size_t LogTest::initial_offset_record_sizes_[] =
-    {10000,  // Two sizable records in first block
-     10000,
-     2 * log::kBlockSize - 1000,  // Span three blocks
-     1};
+size_t LogTest::initial_offset_record_sizes_[] = {
+    10000,  // Two sizable records in first block
+    10000,
+    2 * log::kBlockSize - 1000,  // Span three blocks
+    1,
+    13716,                          // Consume all but two bytes of block 3.
+    log::kBlockSize - kHeaderSize,  // Consume the entirety of block 4.
+};
 
-uint64_t LogTest::initial_offset_last_record_offsets_[] =
-    {0,
-     kHeaderSize + 10000,
-     2 * (kHeaderSize + 10000),
-     2 * (kHeaderSize + 10000) +
-         (2 * log::kBlockSize - 1000) + 3 * kHeaderSize};
+uint64_t LogTest::initial_offset_last_record_offsets_[] = {
+    0,
+    kHeaderSize + 10000,
+    2 * (kHeaderSize + 10000),
+    2 * (kHeaderSize + 10000) + (2 * log::kBlockSize - 1000) + 3 * kHeaderSize,
+    2 * (kHeaderSize + 10000) + (2 * log::kBlockSize - 1000) + 3 * kHeaderSize +
+        kHeaderSize + 1,
+    3 * log::kBlockSize,
+};
 
+// LogTest::initial_offset_last_record_offsets_ must be defined before this.
+int LogTest::num_initial_offset_records_ =
+    sizeof(LogTest::initial_offset_last_record_offsets_) / sizeof(uint64_t);
 
-TEST(LogTest, Empty) {
-  ASSERT_EQ("EOF", Read());
-}
+TEST(LogTest, Empty) { ASSERT_EQ("EOF", Read()); }
 
 TEST(LogTest, ReadWrite) {
   Write("foo");
@@ -274,7 +295,7 @@ TEST(LogTest, Fragmentation) {
 
 TEST(LogTest, MarginalTrailer) {
   // Make a trailer that is exactly the same length as an empty record.
-  const int n = kBlockSize - 2*kHeaderSize;
+  const int n = kBlockSize - 2 * kHeaderSize;
   Write(BigString("foo", n));
   ASSERT_EQ(kBlockSize - kHeaderSize, WrittenBytes());
   Write("");
@@ -287,7 +308,7 @@ TEST(LogTest, MarginalTrailer) {
 
 TEST(LogTest, MarginalTrailer2) {
   // Make a trailer that is exactly the same length as an empty record.
-  const int n = kBlockSize - 2*kHeaderSize;
+  const int n = kBlockSize - 2 * kHeaderSize;
   Write(BigString("foo", n));
   ASSERT_EQ(kBlockSize - kHeaderSize, WrittenBytes());
   Write("bar");
@@ -299,7 +320,7 @@ TEST(LogTest, MarginalTrailer2) {
 }
 
 TEST(LogTest, ShortTrailer) {
-  const int n = kBlockSize - 2*kHeaderSize + 4;
+  const int n = kBlockSize - 2 * kHeaderSize + 4;
   Write(BigString("foo", n));
   ASSERT_EQ(kBlockSize - kHeaderSize + 4, WrittenBytes());
   Write("");
@@ -311,13 +332,22 @@ TEST(LogTest, ShortTrailer) {
 }
 
 TEST(LogTest, AlignedEof) {
-  const int n = kBlockSize - 2*kHeaderSize + 4;
+  const int n = kBlockSize - 2 * kHeaderSize + 4;
   Write(BigString("foo", n));
   ASSERT_EQ(kBlockSize - kHeaderSize + 4, WrittenBytes());
   ASSERT_EQ(BigString("foo", n), Read());
   ASSERT_EQ("EOF", Read());
 }
 
+TEST(LogTest, OpenForAppend) {
+  Write("hello");
+  ReopenForAppend();
+  Write("world");
+  ASSERT_EQ("hello", Read());
+  ASSERT_EQ("world", Read());
+  ASSERT_EQ("EOF", Read());
+}
+
 TEST(LogTest, RandomRead) {
   const int N = 500;
   Random write_rnd(301);
@@ -353,7 +383,7 @@ TEST(LogTest, BadRecordType) {
 
 TEST(LogTest, TruncatedTrailingRecordIsIgnored) {
   Write("foo");
-  ShrinkSize(4);   // Drop all payload as well as a header byte
+  ShrinkSize(4);  // Drop all payload as well as a header byte
   ASSERT_EQ("EOF", Read());
   // Truncated last record is ignored, not treated as an error.
   ASSERT_EQ(0, DroppedBytes());
@@ -445,6 +475,22 @@ TEST(LogTest, PartialLastIsIgnored) {
   ASSERT_EQ(0, DroppedBytes());
 }
 
+TEST(LogTest, SkipIntoMultiRecord) {
+  // Consider a fragmented record:
+  //    first(R1), middle(R1), last(R1), first(R2)
+  // If initial_offset points to a record after first(R1) but before first(R2)
+  // incomplete fragment errors are not actual errors, and must be suppressed
+  // until a new first or full record is encountered.
+  Write(BigString("foo", 3 * kBlockSize));
+  Write("correct");
+  StartReadingAt(kBlockSize);
+
+  ASSERT_EQ("correct", Read());
+  ASSERT_EQ("", ReportMessage());
+  ASSERT_EQ(0, DroppedBytes());
+  ASSERT_EQ("EOF", Read());
+}
+
 TEST(LogTest, ErrorJoinsRecords) {
   // Consider two fragmented records:
   //    first(R1) last(R1) first(R2) last(R2)
@@ -457,44 +503,30 @@ TEST(LogTest, ErrorJoinsRecords) {
   Write("correct");
 
   // Wipe the middle block
-  for (int offset = kBlockSize; offset < 2*kBlockSize; offset++) {
+  for (int offset = kBlockSize; offset < 2 * kBlockSize; offset++) {
     SetByte(offset, 'x');
   }
 
   ASSERT_EQ("correct", Read());
   ASSERT_EQ("EOF", Read());
   const size_t dropped = DroppedBytes();
-  ASSERT_LE(dropped, 2*kBlockSize + 100);
-  ASSERT_GE(dropped, 2*kBlockSize);
+  ASSERT_LE(dropped, 2 * kBlockSize + 100);
+  ASSERT_GE(dropped, 2 * kBlockSize);
 }
 
-TEST(LogTest, ReadStart) {
-  CheckInitialOffsetRecord(0, 0);
-}
+TEST(LogTest, ReadStart) { CheckInitialOffsetRecord(0, 0); }
 
-TEST(LogTest, ReadSecondOneOff) {
-  CheckInitialOffsetRecord(1, 1);
-}
+TEST(LogTest, ReadSecondOneOff) { CheckInitialOffsetRecord(1, 1); }
 
-TEST(LogTest, ReadSecondTenThousand) {
-  CheckInitialOffsetRecord(10000, 1);
-}
+TEST(LogTest, ReadSecondTenThousand) { CheckInitialOffsetRecord(10000, 1); }
 
-TEST(LogTest, ReadSecondStart) {
-  CheckInitialOffsetRecord(10007, 1);
-}
+TEST(LogTest, ReadSecondStart) { CheckInitialOffsetRecord(10007, 1); }
 
-TEST(LogTest, ReadThirdOneOff) {
-  CheckInitialOffsetRecord(10008, 2);
-}
+TEST(LogTest, ReadThirdOneOff) { CheckInitialOffsetRecord(10008, 2); }
 
-TEST(LogTest, ReadThirdStart) {
-  CheckInitialOffsetRecord(20014, 2);
-}
+TEST(LogTest, ReadThirdStart) { CheckInitialOffsetRecord(20014, 2); }
 
-TEST(LogTest, ReadFourthOneOff) {
-  CheckInitialOffsetRecord(20015, 3);
-}
+TEST(LogTest, ReadFourthOneOff) { CheckInitialOffsetRecord(20015, 3); }
 
 TEST(LogTest, ReadFourthFirstBlockTrailer) {
   CheckInitialOffsetRecord(log::kBlockSize - 4, 3);
@@ -514,17 +546,15 @@ TEST(LogTest, ReadFourthStart) {
       3);
 }
 
-TEST(LogTest, ReadEnd) {
-  CheckOffsetPastEndReturnsNoRecords(0);
+TEST(LogTest, ReadInitialOffsetIntoBlockPadding) {
+  CheckInitialOffsetRecord(3 * log::kBlockSize - 3, 5);
 }
 
-TEST(LogTest, ReadPastEnd) {
-  CheckOffsetPastEndReturnsNoRecords(5);
-}
+TEST(LogTest, ReadEnd) { CheckOffsetPastEndReturnsNoRecords(0); }
+
+TEST(LogTest, ReadPastEnd) { CheckOffsetPastEndReturnsNoRecords(5); }
 
 }  // namespace log
 }  // namespace leveldb
 
-int main(int argc, char** argv) {
-  return leveldb::test::RunAllTests();
-}
+int main(int argc, char** argv) { return leveldb::test::RunAllTests(); }
diff --git a/db/log_writer.cc b/db/log_writer.cc
index 2da99ac..bfb16fb 100644
--- a/db/log_writer.cc
+++ b/db/log_writer.cc
@@ -5,6 +5,7 @@
 #include "db/log_writer.h"
 
 #include <stdint.h>
+
 #include "leveldb/env.h"
 #include "util/coding.h"
 #include "util/crc32c.h"
@@ -12,18 +13,24 @@
 namespace leveldb {
 namespace log {
 
-Writer::Writer(WritableFile* dest)
-    : dest_(dest),
-      block_offset_(0) {
+static void InitTypeCrc(uint32_t* type_crc) {
   for (int i = 0; i <= kMaxRecordType; i++) {
     char t = static_cast<char>(i);
-    type_crc_[i] = crc32c::Value(&t, 1);
+    type_crc[i] = crc32c::Value(&t, 1);
   }
 }
 
-Writer::~Writer() {
+Writer::Writer(WritableFile* dest) : dest_(dest), block_offset_(0) {
+  InitTypeCrc(type_crc_);
+}
+
+Writer::Writer(WritableFile* dest, uint64_t dest_length)
+    : dest_(dest), block_offset_(dest_length % kBlockSize) {
+  InitTypeCrc(type_crc_);
 }
 
+Writer::~Writer() = default;
+
 Status Writer::AddRecord(const Slice& slice) {
   const char* ptr = slice.data();
   size_t left = slice.size();
@@ -40,7 +47,7 @@ Status Writer::AddRecord(const Slice& slice) {
       // Switch to a new block
       if (leftover > 0) {
         // Fill the trailer (literal below relies on kHeaderSize being 7)
-        assert(kHeaderSize == 7);
+        static_assert(kHeaderSize == 7, "");
         dest_->Append(Slice("\x00\x00\x00\x00\x00\x00", leftover));
       }
       block_offset_ = 0;
@@ -72,30 +79,31 @@ Status Writer::AddRecord(const Slice& slice) {
   return s;
 }
 
-Status Writer::EmitPhysicalRecord(RecordType t, const char* ptr, size_t n) {
-  assert(n <= 0xffff);  // Must fit in two bytes
-  assert(block_offset_ + kHeaderSize + n <= kBlockSize);
+Status Writer::EmitPhysicalRecord(RecordType t, const char* ptr,
+                                  size_t length) {
+  assert(length <= 0xffff);  // Must fit in two bytes
+  assert(block_offset_ + kHeaderSize + length <= kBlockSize);
 
   // Format the header
   char buf[kHeaderSize];
-  buf[4] = static_cast<char>(n & 0xff);
-  buf[5] = static_cast<char>(n >> 8);
+  buf[4] = static_cast<char>(length & 0xff);
+  buf[5] = static_cast<char>(length >> 8);
   buf[6] = static_cast<char>(t);
 
   // Compute the crc of the record type and the payload.
-  uint32_t crc = crc32c::Extend(type_crc_[t], ptr, n);
-  crc = crc32c::Mask(crc);                 // Adjust for storage
+  uint32_t crc = crc32c::Extend(type_crc_[t], ptr, length);
+  crc = crc32c::Mask(crc);  // Adjust for storage
   EncodeFixed32(buf, crc);
 
   // Write the header and the payload
   Status s = dest_->Append(Slice(buf, kHeaderSize));
   if (s.ok()) {
-    s = dest_->Append(Slice(ptr, n));
+    s = dest_->Append(Slice(ptr, length));
     if (s.ok()) {
       s = dest_->Flush();
     }
   }
-  block_offset_ += kHeaderSize + n;
+  block_offset_ += kHeaderSize + length;
   return s;
 }
 
diff --git a/db/log_writer.h b/db/log_writer.h
index a3a954d..c0a2114 100644
--- a/db/log_writer.h
+++ b/db/log_writer.h
@@ -6,6 +6,7 @@
 #define STORAGE_LEVELDB_DB_LOG_WRITER_H_
 
 #include <stdint.h>
+
 #include "db/log_format.h"
 #include "leveldb/slice.h"
 #include "leveldb/status.h"
@@ -22,24 +23,29 @@ class Writer {
   // "*dest" must be initially empty.
   // "*dest" must remain live while this Writer is in use.
   explicit Writer(WritableFile* dest);
+
+  // Create a writer that will append data to "*dest".
+  // "*dest" must have initial length "dest_length".
+  // "*dest" must remain live while this Writer is in use.
+  Writer(WritableFile* dest, uint64_t dest_length);
+
+  Writer(const Writer&) = delete;
+  Writer& operator=(const Writer&) = delete;
+
   ~Writer();
 
   Status AddRecord(const Slice& slice);
 
  private:
+  Status EmitPhysicalRecord(RecordType type, const char* ptr, size_t length);
+
   WritableFile* dest_;
-  int block_offset_;       // Current offset in block
+  int block_offset_;  // Current offset in block
 
   // crc32c values for all supported record types.  These are
   // pre-computed to reduce the overhead of computing the crc of the
   // record type stored in the header.
   uint32_t type_crc_[kMaxRecordType + 1];
-
-  Status EmitPhysicalRecord(RecordType type, const char* ptr, size_t length);
-
-  // No copying allowed
-  Writer(const Writer&);
-  void operator=(const Writer&);
 };
 
 }  // namespace log
diff --git a/db/memtable.cc b/db/memtable.cc
index bfec0a7..00931d4 100644
--- a/db/memtable.cc
+++ b/db/memtable.cc
@@ -18,20 +18,15 @@ static Slice GetLengthPrefixedSlice(const char* data) {
   return Slice(p, len);
 }
 
-MemTable::MemTable(const InternalKeyComparator& cmp)
-    : comparator_(cmp),
-      refs_(0),
-      table_(comparator_, &arena_) {
-}
+MemTable::MemTable(const InternalKeyComparator& comparator)
+    : comparator_(comparator), refs_(0), table_(comparator_, &arena_) {}
 
-MemTable::~MemTable() {
-  assert(refs_ == 0);
-}
+MemTable::~MemTable() { assert(refs_ == 0); }
 
 size_t MemTable::ApproximateMemoryUsage() { return arena_.MemoryUsage(); }
 
-int MemTable::KeyComparator::operator()(const char* aptr, const char* bptr)
-    const {
+int MemTable::KeyComparator::operator()(const char* aptr,
+                                        const char* bptr) const {
   // Internal keys are encoded as length-prefixed strings.
   Slice a = GetLengthPrefixedSlice(aptr);
   Slice b = GetLengthPrefixedSlice(bptr);
@@ -48,39 +43,37 @@ static const char* EncodeKey(std::string* scratch, const Slice& target) {
   return scratch->data();
 }
 
-class MemTableIterator: public Iterator {
+class MemTableIterator : public Iterator {
  public:
-  explicit MemTableIterator(MemTable::Table* table) : iter_(table) { }
-
-  virtual bool Valid() const { return iter_.Valid(); }
-  virtual void Seek(const Slice& k) { iter_.Seek(EncodeKey(&tmp_, k)); }
-  virtual void SeekToFirst() { iter_.SeekToFirst(); }
-  virtual void SeekToLast() { iter_.SeekToLast(); }
-  virtual void Next() { iter_.Next(); }
-  virtual void Prev() { iter_.Prev(); }
-  virtual Slice key() const { return GetLengthPrefixedSlice(iter_.key()); }
-  virtual Slice value() const {
+  explicit MemTableIterator(MemTable::Table* table) : iter_(table) {}
+
+  MemTableIterator(const MemTableIterator&) = delete;
+  MemTableIterator& operator=(const MemTableIterator&) = delete;
+
+  ~MemTableIterator() override = default;
+
+  bool Valid() const override { return iter_.Valid(); }
+  void Seek(const Slice& k) override { iter_.Seek(EncodeKey(&tmp_, k)); }
+  void SeekToFirst() override { iter_.SeekToFirst(); }
+  void SeekToLast() override { iter_.SeekToLast(); }
+  void Next() override { iter_.Next(); }
+  void Prev() override { iter_.Prev(); }
+  Slice key() const override { return GetLengthPrefixedSlice(iter_.key()); }
+  Slice value() const override {
     Slice key_slice = GetLengthPrefixedSlice(iter_.key());
     return GetLengthPrefixedSlice(key_slice.data() + key_slice.size());
   }
 
-  virtual Status status() const { return Status::OK(); }
+  Status status() const override { return Status::OK(); }
 
  private:
   MemTable::Table::Iterator iter_;
-  std::string tmp_;       // For passing to EncodeKey
-
-  // No copying allowed
-  MemTableIterator(const MemTableIterator&);
-  void operator=(const MemTableIterator&);
+  std::string tmp_;  // For passing to EncodeKey
 };
 
-Iterator* MemTable::NewIterator() {
-  return new MemTableIterator(&table_);
-}
+Iterator* MemTable::NewIterator() { return new MemTableIterator(&table_); }
 
-void MemTable::Add(SequenceNumber s, ValueType type,
-                   const Slice& key,
+void MemTable::Add(SequenceNumber s, ValueType type, const Slice& key,
                    const Slice& value) {
   // Format of an entry is concatenation of:
   //  key_size     : varint32 of internal_key.size()
@@ -90,9 +83,9 @@ void MemTable::Add(SequenceNumber s, ValueType type,
   size_t key_size = key.size();
   size_t val_size = value.size();
   size_t internal_key_size = key_size + 8;
-  const size_t encoded_len =
-      VarintLength(internal_key_size) + internal_key_size +
-      VarintLength(val_size) + val_size;
+  const size_t encoded_len = VarintLength(internal_key_size) +
+                             internal_key_size + VarintLength(val_size) +
+                             val_size;
   char* buf = arena_.Allocate(encoded_len);
   char* p = EncodeVarint32(buf, internal_key_size);
   memcpy(p, key.data(), key_size);
@@ -101,7 +94,7 @@ void MemTable::Add(SequenceNumber s, ValueType type,
   p += 8;
   p = EncodeVarint32(p, val_size);
   memcpy(p, value.data(), val_size);
-  assert((p + val_size) - buf == encoded_len);
+  assert(p + val_size == buf + encoded_len);
   table_.Insert(buf);
 }
 
@@ -121,10 +114,9 @@ bool MemTable::Get(const LookupKey& key, std::string* value, Status* s) {
     // all entries with overly large sequence numbers.
     const char* entry = iter.key();
     uint32_t key_length;
-    const char* key_ptr = GetVarint32Ptr(entry, entry+5, &key_length);
+    const char* key_ptr = GetVarint32Ptr(entry, entry + 5, &key_length);
     if (comparator_.comparator.user_comparator()->Compare(
-            Slice(key_ptr, key_length - 8),
-            key.user_key()) == 0) {
+            Slice(key_ptr, key_length - 8), key.user_key()) == 0) {
       // Correct user key
       const uint64_t tag = DecodeFixed64(key_ptr + key_length - 8);
       switch (static_cast<ValueType>(tag & 0xff)) {
diff --git a/db/memtable.h b/db/memtable.h
index 92e90bb..9d986b1 100644
--- a/db/memtable.h
+++ b/db/memtable.h
@@ -6,15 +6,15 @@
 #define STORAGE_LEVELDB_DB_MEMTABLE_H_
 
 #include <string>
-#include "leveldb/db.h"
+
 #include "db/dbformat.h"
 #include "db/skiplist.h"
+#include "leveldb/db.h"
 #include "util/arena.h"
 
 namespace leveldb {
 
 class InternalKeyComparator;
-class Mutex;
 class MemTableIterator;
 
 class MemTable {
@@ -23,6 +23,9 @@ class MemTable {
   // is zero and the caller must call Ref() at least once.
   explicit MemTable(const InternalKeyComparator& comparator);
 
+  MemTable(const MemTable&) = delete;
+  MemTable& operator=(const MemTable&) = delete;
+
   // Increase reference count.
   void Ref() { ++refs_; }
 
@@ -36,10 +39,7 @@ class MemTable {
   }
 
   // Returns an estimate of the number of bytes of data in use by this
-  // data structure.
-  //
-  // REQUIRES: external synchronization to prevent simultaneous
-  // operations on the same MemTable.
+  // data structure. It is safe to call when MemTable is being modified.
   size_t ApproximateMemoryUsage();
 
   // Return an iterator that yields the contents of the memtable.
@@ -53,8 +53,7 @@ class MemTable {
   // Add an entry into memtable that maps key to value at the
   // specified sequence number and with the specified type.
   // Typically value will be empty if type==kTypeDeletion.
-  void Add(SequenceNumber seq, ValueType type,
-           const Slice& key,
+  void Add(SequenceNumber seq, ValueType type, const Slice& key,
            const Slice& value);
 
   // If memtable contains a value for key, store it in *value and return true.
@@ -64,26 +63,23 @@ class MemTable {
   bool Get(const LookupKey& key, std::string* value, Status* s);
 
  private:
-  ~MemTable();  // Private since only Unref() should be used to delete it
+  friend class MemTableIterator;
+  friend class MemTableBackwardIterator;
 
   struct KeyComparator {
     const InternalKeyComparator comparator;
-    explicit KeyComparator(const InternalKeyComparator& c) : comparator(c) { }
+    explicit KeyComparator(const InternalKeyComparator& c) : comparator(c) {}
     int operator()(const char* a, const char* b) const;
   };
-  friend class MemTableIterator;
-  friend class MemTableBackwardIterator;
 
   typedef SkipList<const char*, KeyComparator> Table;
 
+  ~MemTable();  // Private since only Unref() should be used to delete it
+
   KeyComparator comparator_;
   int refs_;
   Arena arena_;
   Table table_;
-
-  // No copying allowed
-  MemTable(const MemTable&);
-  void operator=(const MemTable&);
 };
 
 }  // namespace leveldb
diff --git a/db/recovery_test.cc b/db/recovery_test.cc
new file mode 100644
index 0000000..547a959
--- /dev/null
+++ b/db/recovery_test.cc
@@ -0,0 +1,330 @@
+// Copyright (c) 2014 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#include "db/db_impl.h"
+#include "db/filename.h"
+#include "db/version_set.h"
+#include "db/write_batch_internal.h"
+#include "leveldb/db.h"
+#include "leveldb/env.h"
+#include "leveldb/write_batch.h"
+#include "util/logging.h"
+#include "util/testharness.h"
+#include "util/testutil.h"
+
+namespace leveldb {
+
+class RecoveryTest {
+ public:
+  RecoveryTest() : env_(Env::Default()), db_(nullptr) {
+    dbname_ = test::TmpDir() + "/recovery_test";
+    DestroyDB(dbname_, Options());
+    Open();
+  }
+
+  ~RecoveryTest() {
+    Close();
+    DestroyDB(dbname_, Options());
+  }
+
+  DBImpl* dbfull() const { return reinterpret_cast<DBImpl*>(db_); }
+  Env* env() const { return env_; }
+
+  bool CanAppend() {
+    WritableFile* tmp;
+    Status s = env_->NewAppendableFile(CurrentFileName(dbname_), &tmp);
+    delete tmp;
+    if (s.IsNotSupportedError()) {
+      return false;
+    } else {
+      return true;
+    }
+  }
+
+  void Close() {
+    delete db_;
+    db_ = nullptr;
+  }
+
+  Status OpenWithStatus(Options* options = nullptr) {
+    Close();
+    Options opts;
+    if (options != nullptr) {
+      opts = *options;
+    } else {
+      opts.reuse_logs = true;  // TODO(sanjay): test both ways
+      opts.create_if_missing = true;
+    }
+    if (opts.env == nullptr) {
+      opts.env = env_;
+    }
+    return DB::Open(opts, dbname_, &db_);
+  }
+
+  void Open(Options* options = nullptr) {
+    ASSERT_OK(OpenWithStatus(options));
+    ASSERT_EQ(1, NumLogs());
+  }
+
+  Status Put(const std::string& k, const std::string& v) {
+    return db_->Put(WriteOptions(), k, v);
+  }
+
+  std::string Get(const std::string& k, const Snapshot* snapshot = nullptr) {
+    std::string result;
+    Status s = db_->Get(ReadOptions(), k, &result);
+    if (s.IsNotFound()) {
+      result = "NOT_FOUND";
+    } else if (!s.ok()) {
+      result = s.ToString();
+    }
+    return result;
+  }
+
+  std::string ManifestFileName() {
+    std::string current;
+    ASSERT_OK(ReadFileToString(env_, CurrentFileName(dbname_), &current));
+    size_t len = current.size();
+    if (len > 0 && current[len - 1] == '\n') {
+      current.resize(len - 1);
+    }
+    return dbname_ + "/" + current;
+  }
+
+  std::string LogName(uint64_t number) { return LogFileName(dbname_, number); }
+
+  size_t DeleteLogFiles() {
+    // Linux allows unlinking open files, but Windows does not.
+    // Closing the db allows for file deletion.
+    Close();
+    std::vector<uint64_t> logs = GetFiles(kLogFile);
+    for (size_t i = 0; i < logs.size(); i++) {
+      ASSERT_OK(env_->DeleteFile(LogName(logs[i]))) << LogName(logs[i]);
+    }
+    return logs.size();
+  }
+
+  void DeleteManifestFile() { ASSERT_OK(env_->DeleteFile(ManifestFileName())); }
+
+  uint64_t FirstLogFile() { return GetFiles(kLogFile)[0]; }
+
+  std::vector<uint64_t> GetFiles(FileType t) {
+    std::vector<std::string> filenames;
+    ASSERT_OK(env_->GetChildren(dbname_, &filenames));
+    std::vector<uint64_t> result;
+    for (size_t i = 0; i < filenames.size(); i++) {
+      uint64_t number;
+      FileType type;
+      if (ParseFileName(filenames[i], &number, &type) && type == t) {
+        result.push_back(number);
+      }
+    }
+    return result;
+  }
+
+  int NumLogs() { return GetFiles(kLogFile).size(); }
+
+  int NumTables() { return GetFiles(kTableFile).size(); }
+
+  uint64_t FileSize(const std::string& fname) {
+    uint64_t result;
+    ASSERT_OK(env_->GetFileSize(fname, &result)) << fname;
+    return result;
+  }
+
+  void CompactMemTable() { dbfull()->TEST_CompactMemTable(); }
+
+  // Directly construct a log file that sets key to val.
+  void MakeLogFile(uint64_t lognum, SequenceNumber seq, Slice key, Slice val) {
+    std::string fname = LogFileName(dbname_, lognum);
+    WritableFile* file;
+    ASSERT_OK(env_->NewWritableFile(fname, &file));
+    log::Writer writer(file);
+    WriteBatch batch;
+    batch.Put(key, val);
+    WriteBatchInternal::SetSequence(&batch, seq);
+    ASSERT_OK(writer.AddRecord(WriteBatchInternal::Contents(&batch)));
+    ASSERT_OK(file->Flush());
+    delete file;
+  }
+
+ private:
+  std::string dbname_;
+  Env* env_;
+  DB* db_;
+};
+
+TEST(RecoveryTest, ManifestReused) {
+  if (!CanAppend()) {
+    fprintf(stderr, "skipping test because env does not support appending\n");
+    return;
+  }
+  ASSERT_OK(Put("foo", "bar"));
+  Close();
+  std::string old_manifest = ManifestFileName();
+  Open();
+  ASSERT_EQ(old_manifest, ManifestFileName());
+  ASSERT_EQ("bar", Get("foo"));
+  Open();
+  ASSERT_EQ(old_manifest, ManifestFileName());
+  ASSERT_EQ("bar", Get("foo"));
+}
+
+TEST(RecoveryTest, LargeManifestCompacted) {
+  if (!CanAppend()) {
+    fprintf(stderr, "skipping test because env does not support appending\n");
+    return;
+  }
+  ASSERT_OK(Put("foo", "bar"));
+  Close();
+  std::string old_manifest = ManifestFileName();
+
+  // Pad with zeroes to make manifest file very big.
+  {
+    uint64_t len = FileSize(old_manifest);
+    WritableFile* file;
+    ASSERT_OK(env()->NewAppendableFile(old_manifest, &file));
+    std::string zeroes(3 * 1048576 - static_cast<size_t>(len), 0);
+    ASSERT_OK(file->Append(zeroes));
+    ASSERT_OK(file->Flush());
+    delete file;
+  }
+
+  Open();
+  std::string new_manifest = ManifestFileName();
+  ASSERT_NE(old_manifest, new_manifest);
+  ASSERT_GT(10000, FileSize(new_manifest));
+  ASSERT_EQ("bar", Get("foo"));
+
+  Open();
+  ASSERT_EQ(new_manifest, ManifestFileName());
+  ASSERT_EQ("bar", Get("foo"));
+}
+
+TEST(RecoveryTest, NoLogFiles) {
+  ASSERT_OK(Put("foo", "bar"));
+  ASSERT_EQ(1, DeleteLogFiles());
+  Open();
+  ASSERT_EQ("NOT_FOUND", Get("foo"));
+  Open();
+  ASSERT_EQ("NOT_FOUND", Get("foo"));
+}
+
+TEST(RecoveryTest, LogFileReuse) {
+  if (!CanAppend()) {
+    fprintf(stderr, "skipping test because env does not support appending\n");
+    return;
+  }
+  for (int i = 0; i < 2; i++) {
+    ASSERT_OK(Put("foo", "bar"));
+    if (i == 0) {
+      // Compact to ensure current log is empty
+      CompactMemTable();
+    }
+    Close();
+    ASSERT_EQ(1, NumLogs());
+    uint64_t number = FirstLogFile();
+    if (i == 0) {
+      ASSERT_EQ(0, FileSize(LogName(number)));
+    } else {
+      ASSERT_LT(0, FileSize(LogName(number)));
+    }
+    Open();
+    ASSERT_EQ(1, NumLogs());
+    ASSERT_EQ(number, FirstLogFile()) << "did not reuse log file";
+    ASSERT_EQ("bar", Get("foo"));
+    Open();
+    ASSERT_EQ(1, NumLogs());
+    ASSERT_EQ(number, FirstLogFile()) << "did not reuse log file";
+    ASSERT_EQ("bar", Get("foo"));
+  }
+}
+
+TEST(RecoveryTest, MultipleMemTables) {
+  // Make a large log.
+  const int kNum = 1000;
+  for (int i = 0; i < kNum; i++) {
+    char buf[100];
+    snprintf(buf, sizeof(buf), "%050d", i);
+    ASSERT_OK(Put(buf, buf));
+  }
+  ASSERT_EQ(0, NumTables());
+  Close();
+  ASSERT_EQ(0, NumTables());
+  ASSERT_EQ(1, NumLogs());
+  uint64_t old_log_file = FirstLogFile();
+
+  // Force creation of multiple memtables by reducing the write buffer size.
+  Options opt;
+  opt.reuse_logs = true;
+  opt.write_buffer_size = (kNum * 100) / 2;
+  Open(&opt);
+  ASSERT_LE(2, NumTables());
+  ASSERT_EQ(1, NumLogs());
+  ASSERT_NE(old_log_file, FirstLogFile()) << "must not reuse log";
+  for (int i = 0; i < kNum; i++) {
+    char buf[100];
+    snprintf(buf, sizeof(buf), "%050d", i);
+    ASSERT_EQ(buf, Get(buf));
+  }
+}
+
+TEST(RecoveryTest, MultipleLogFiles) {
+  ASSERT_OK(Put("foo", "bar"));
+  Close();
+  ASSERT_EQ(1, NumLogs());
+
+  // Make a bunch of uncompacted log files.
+  uint64_t old_log = FirstLogFile();
+  MakeLogFile(old_log + 1, 1000, "hello", "world");
+  MakeLogFile(old_log + 2, 1001, "hi", "there");
+  MakeLogFile(old_log + 3, 1002, "foo", "bar2");
+
+  // Recover and check that all log files were processed.
+  Open();
+  ASSERT_LE(1, NumTables());
+  ASSERT_EQ(1, NumLogs());
+  uint64_t new_log = FirstLogFile();
+  ASSERT_LE(old_log + 3, new_log);
+  ASSERT_EQ("bar2", Get("foo"));
+  ASSERT_EQ("world", Get("hello"));
+  ASSERT_EQ("there", Get("hi"));
+
+  // Test that previous recovery produced recoverable state.
+  Open();
+  ASSERT_LE(1, NumTables());
+  ASSERT_EQ(1, NumLogs());
+  if (CanAppend()) {
+    ASSERT_EQ(new_log, FirstLogFile());
+  }
+  ASSERT_EQ("bar2", Get("foo"));
+  ASSERT_EQ("world", Get("hello"));
+  ASSERT_EQ("there", Get("hi"));
+
+  // Check that introducing an older log file does not cause it to be re-read.
+  Close();
+  MakeLogFile(old_log + 1, 2000, "hello", "stale write");
+  Open();
+  ASSERT_LE(1, NumTables());
+  ASSERT_EQ(1, NumLogs());
+  if (CanAppend()) {
+    ASSERT_EQ(new_log, FirstLogFile());
+  }
+  ASSERT_EQ("bar2", Get("foo"));
+  ASSERT_EQ("world", Get("hello"));
+  ASSERT_EQ("there", Get("hi"));
+}
+
+TEST(RecoveryTest, ManifestMissing) {
+  ASSERT_OK(Put("foo", "bar"));
+  Close();
+  DeleteManifestFile();
+
+  Status status = OpenWithStatus();
+  ASSERT_TRUE(status.IsCorruption());
+}
+
+}  // namespace leveldb
+
+int main(int argc, char** argv) { return leveldb::test::RunAllTests(); }
diff --git a/db/repair.cc b/db/repair.cc
index 4cd4bb0..d9d12ba 100644
--- a/db/repair.cc
+++ b/db/repair.cc
@@ -54,7 +54,7 @@ class Repairer {
         owns_cache_(options_.block_cache != options.block_cache),
         next_file_number_(1) {
     // TableCache can be small since we expect each table to be opened once.
-    table_cache_ = new TableCache(dbname_, &options_, 10);
+    table_cache_ = new TableCache(dbname_, options_, 10);
   }
 
   ~Repairer() {
@@ -84,9 +84,7 @@ class Repairer {
           "recovered %d files; %llu bytes. "
           "Some data may have been lost. "
           "****",
-          dbname_.c_str(),
-          static_cast<int>(tables_.size()),
-          bytes);
+          dbname_.c_str(), static_cast<int>(tables_.size()), bytes);
     }
     return status;
   }
@@ -97,22 +95,6 @@ class Repairer {
     SequenceNumber max_sequence;
   };
 
-  std::string const dbname_;
-  Env* const env_;
-  InternalKeyComparator const icmp_;
-  InternalFilterPolicy const ipolicy_;
-  Options const options_;
-  bool owns_info_log_;
-  bool owns_cache_;
-  TableCache* table_cache_;
-  VersionEdit edit_;
-
-  std::vector<std::string> manifests_;
-  std::vector<uint64_t> table_numbers_;
-  std::vector<uint64_t> logs_;
-  std::vector<TableInfo> tables_;
-  uint64_t next_file_number_;
-
   Status FindFiles() {
     std::vector<std::string> filenames;
     Status status = env_->GetChildren(dbname_, &filenames);
@@ -152,8 +134,7 @@ class Repairer {
       Status status = ConvertLogToTable(logs_[i]);
       if (!status.ok()) {
         Log(options_.info_log, "Log #%llu: ignoring conversion error: %s",
-            (unsigned long long) logs_[i],
-            status.ToString().c_str());
+            (unsigned long long)logs_[i], status.ToString().c_str());
       }
       ArchiveFile(logname);
     }
@@ -164,11 +145,10 @@ class Repairer {
       Env* env;
       Logger* info_log;
       uint64_t lognum;
-      virtual void Corruption(size_t bytes, const Status& s) {
+      void Corruption(size_t bytes, const Status& s) override {
         // We print error messages for corruption, but continue repairing.
         Log(info_log, "Log #%llu: dropping %d bytes; %s",
-            (unsigned long long) lognum,
-            static_cast<int>(bytes),
+            (unsigned long long)lognum, static_cast<int>(bytes),
             s.ToString().c_str());
       }
     };
@@ -190,8 +170,8 @@ class Repairer {
     // corruptions cause entire commits to be skipped instead of
     // propagating bad information (like overly large sequence
     // numbers).
-    log::Reader reader(lfile, &reporter, false/*do not checksum*/,
-                       0/*initial_offset*/);
+    log::Reader reader(lfile, &reporter, false /*do not checksum*/,
+                       0 /*initial_offset*/);
 
     // Read all the records and add to a memtable
     std::string scratch;
@@ -202,8 +182,8 @@ class Repairer {
     int counter = 0;
     while (reader.ReadRecord(&record, &scratch)) {
       if (record.size() < 12) {
-        reporter.Corruption(
-            record.size(), Status::Corruption("log record too small"));
+        reporter.Corruption(record.size(),
+                            Status::Corruption("log record too small"));
         continue;
       }
       WriteBatchInternal::SetContents(&batch, record);
@@ -212,8 +192,7 @@ class Repairer {
         counter += WriteBatchInternal::Count(&batch);
       } else {
         Log(options_.info_log, "Log #%llu: ignoring %s",
-            (unsigned long long) log,
-            status.ToString().c_str());
+            (unsigned long long)log, status.ToString().c_str());
         status = Status::OK();  // Keep going with rest of file
       }
     }
@@ -227,16 +206,14 @@ class Repairer {
     status = BuildTable(dbname_, env_, options_, table_cache_, iter, &meta);
     delete iter;
     mem->Unref();
-    mem = NULL;
+    mem = nullptr;
     if (status.ok()) {
       if (meta.file_size > 0) {
         table_numbers_.push_back(meta.number);
       }
     }
     Log(options_.info_log, "Log #%llu: %d ops saved to Table #%llu %s",
-        (unsigned long long) log,
-        counter,
-        (unsigned long long) meta.number,
+        (unsigned long long)log, counter, (unsigned long long)meta.number,
         status.ToString().c_str());
     return status;
   }
@@ -272,8 +249,7 @@ class Repairer {
       ArchiveFile(TableFileName(dbname_, number));
       ArchiveFile(SSTTableFileName(dbname_, number));
       Log(options_.info_log, "Table #%llu: dropped: %s",
-          (unsigned long long) t.meta.number,
-          status.ToString().c_str());
+          (unsigned long long)t.meta.number, status.ToString().c_str());
       return;
     }
 
@@ -287,8 +263,7 @@ class Repairer {
       Slice key = iter->key();
       if (!ParseInternalKey(key, &parsed)) {
         Log(options_.info_log, "Table #%llu: unparsable key %s",
-            (unsigned long long) t.meta.number,
-            EscapeString(key).c_str());
+            (unsigned long long)t.meta.number, EscapeString(key).c_str());
         continue;
       }
 
@@ -307,9 +282,7 @@ class Repairer {
     }
     delete iter;
     Log(options_.info_log, "Table #%llu: %d entries %s",
-        (unsigned long long) t.meta.number,
-        counter,
-        status.ToString().c_str());
+        (unsigned long long)t.meta.number, counter, status.ToString().c_str());
 
     if (status.ok()) {
       tables_.push_back(t);
@@ -350,20 +323,20 @@ class Repairer {
       }
     }
     delete builder;
-    builder = NULL;
+    builder = nullptr;
 
     if (s.ok()) {
       s = file->Close();
     }
     delete file;
-    file = NULL;
+    file = nullptr;
 
     if (counter > 0 && s.ok()) {
       std::string orig = TableFileName(dbname_, t.meta.number);
       s = env_->RenameFile(copy, orig);
       if (s.ok()) {
         Log(options_.info_log, "Table #%llu: %d entries repaired",
-            (unsigned long long) t.meta.number, counter);
+            (unsigned long long)t.meta.number, counter);
         tables_.push_back(t);
       }
     }
@@ -395,11 +368,11 @@ class Repairer {
     for (size_t i = 0; i < tables_.size(); i++) {
       // TODO(opt): separate out into multiple levels
       const TableInfo& t = tables_[i];
-      edit_.AddFile(0, t.meta.number, t.meta.file_size,
-                    t.meta.smallest, t.meta.largest);
+      edit_.AddFile(0, t.meta.number, t.meta.file_size, t.meta.smallest,
+                    t.meta.largest);
     }
 
-    //fprintf(stderr, "NewDescriptor:\n%s\n", edit_.DebugString().c_str());
+    // fprintf(stderr, "NewDescriptor:\n%s\n", edit_.DebugString().c_str());
     {
       log::Writer log(file);
       std::string record;
@@ -410,7 +383,7 @@ class Repairer {
       status = file->Close();
     }
     delete file;
-    file = NULL;
+    file = nullptr;
 
     if (!status.ok()) {
       env_->DeleteFile(tmp);
@@ -438,18 +411,34 @@ class Repairer {
     //    dir/lost/foo
     const char* slash = strrchr(fname.c_str(), '/');
     std::string new_dir;
-    if (slash != NULL) {
+    if (slash != nullptr) {
       new_dir.assign(fname.data(), slash - fname.data());
     }
     new_dir.append("/lost");
     env_->CreateDir(new_dir);  // Ignore error
     std::string new_file = new_dir;
     new_file.append("/");
-    new_file.append((slash == NULL) ? fname.c_str() : slash + 1);
+    new_file.append((slash == nullptr) ? fname.c_str() : slash + 1);
     Status s = env_->RenameFile(fname, new_file);
-    Log(options_.info_log, "Archiving %s: %s\n",
-        fname.c_str(), s.ToString().c_str());
+    Log(options_.info_log, "Archiving %s: %s\n", fname.c_str(),
+        s.ToString().c_str());
   }
+
+  const std::string dbname_;
+  Env* const env_;
+  InternalKeyComparator const icmp_;
+  InternalFilterPolicy const ipolicy_;
+  const Options options_;
+  bool owns_info_log_;
+  bool owns_cache_;
+  TableCache* table_cache_;
+  VersionEdit edit_;
+
+  std::vector<std::string> manifests_;
+  std::vector<uint64_t> table_numbers_;
+  std::vector<uint64_t> logs_;
+  std::vector<TableInfo> tables_;
+  uint64_t next_file_number_;
 };
 }  // namespace
 
diff --git a/db/skiplist.h b/db/skiplist.h
index 8bd7776..a59b45b 100644
--- a/db/skiplist.h
+++ b/db/skiplist.h
@@ -27,9 +27,10 @@
 //
 // ... prev vs. next pointer ordering ...
 
-#include <assert.h>
-#include <stdlib.h>
-#include "port/port.h"
+#include <atomic>
+#include <cassert>
+#include <cstdlib>
+
 #include "util/arena.h"
 #include "util/random.h"
 
@@ -37,7 +38,7 @@ namespace leveldb {
 
 class Arena;
 
-template<typename Key, class Comparator>
+template <typename Key, class Comparator>
 class SkipList {
  private:
   struct Node;
@@ -48,6 +49,9 @@ class SkipList {
   // must remain allocated for the lifetime of the skiplist object.
   explicit SkipList(Comparator cmp, Arena* arena);
 
+  SkipList(const SkipList&) = delete;
+  SkipList& operator=(const SkipList&) = delete;
+
   // Insert key into the list.
   // REQUIRES: nothing that compares equal to key is currently in the list.
   void Insert(const Key& key);
@@ -97,24 +101,10 @@ class SkipList {
  private:
   enum { kMaxHeight = 12 };
 
-  // Immutable after construction
-  Comparator const compare_;
-  Arena* const arena_;    // Arena used for allocations of nodes
-
-  Node* const head_;
-
-  // Modified only by Insert().  Read racily by readers, but stale
-  // values are ok.
-  port::AtomicPointer max_height_;   // Height of the entire list
-
   inline int GetMaxHeight() const {
-    return static_cast<int>(
-        reinterpret_cast<intptr_t>(max_height_.NoBarrier_Load()));
+    return max_height_.load(std::memory_order_relaxed);
   }
 
-  // Read/written only by Insert().
-  Random rnd_;
-
   Node* NewNode(const Key& key, int height);
   int RandomHeight();
   bool Equal(const Key& a, const Key& b) const { return (compare_(a, b) == 0); }
@@ -123,9 +113,9 @@ class SkipList {
   bool KeyIsAfterNode(const Key& key, Node* n) const;
 
   // Return the earliest node that comes at or after key.
-  // Return NULL if there is no such node.
+  // Return nullptr if there is no such node.
   //
-  // If prev is non-NULL, fills prev[level] with pointer to previous
+  // If prev is non-null, fills prev[level] with pointer to previous
   // node at "level" for every level in [0..max_height_-1].
   Node* FindGreaterOrEqual(const Key& key, Node** prev) const;
 
@@ -137,15 +127,24 @@ class SkipList {
   // Return head_ if list is empty.
   Node* FindLast() const;
 
-  // No copying allowed
-  SkipList(const SkipList&);
-  void operator=(const SkipList&);
+  // Immutable after construction
+  Comparator const compare_;
+  Arena* const arena_;  // Arena used for allocations of nodes
+
+  Node* const head_;
+
+  // Modified only by Insert().  Read racily by readers, but stale
+  // values are ok.
+  std::atomic<int> max_height_;  // Height of the entire list
+
+  // Read/written only by Insert().
+  Random rnd_;
 };
 
 // Implementation details follow
-template<typename Key, class Comparator>
-struct SkipList<Key,Comparator>::Node {
-  explicit Node(const Key& k) : key(k) { }
+template <typename Key, class Comparator>
+struct SkipList<Key, Comparator>::Node {
+  explicit Node(const Key& k) : key(k) {}
 
   Key const key;
 
@@ -155,92 +154,92 @@ struct SkipList<Key,Comparator>::Node {
     assert(n >= 0);
     // Use an 'acquire load' so that we observe a fully initialized
     // version of the returned Node.
-    return reinterpret_cast<Node*>(next_[n].Acquire_Load());
+    return next_[n].load(std::memory_order_acquire);
   }
   void SetNext(int n, Node* x) {
     assert(n >= 0);
     // Use a 'release store' so that anybody who reads through this
     // pointer observes a fully initialized version of the inserted node.
-    next_[n].Release_Store(x);
+    next_[n].store(x, std::memory_order_release);
   }
 
   // No-barrier variants that can be safely used in a few locations.
   Node* NoBarrier_Next(int n) {
     assert(n >= 0);
-    return reinterpret_cast<Node*>(next_[n].NoBarrier_Load());
+    return next_[n].load(std::memory_order_relaxed);
   }
   void NoBarrier_SetNext(int n, Node* x) {
     assert(n >= 0);
-    next_[n].NoBarrier_Store(x);
+    next_[n].store(x, std::memory_order_relaxed);
   }
 
  private:
   // Array of length equal to the node height.  next_[0] is lowest level link.
-  port::AtomicPointer next_[1];
+  std::atomic<Node*> next_[1];
 };
 
-template<typename Key, class Comparator>
-typename SkipList<Key,Comparator>::Node*
-SkipList<Key,Comparator>::NewNode(const Key& key, int height) {
-  char* mem = arena_->AllocateAligned(
-      sizeof(Node) + sizeof(port::AtomicPointer) * (height - 1));
-  return new (mem) Node(key);
+template <typename Key, class Comparator>
+typename SkipList<Key, Comparator>::Node* SkipList<Key, Comparator>::NewNode(
+    const Key& key, int height) {
+  char* const node_memory = arena_->AllocateAligned(
+      sizeof(Node) + sizeof(std::atomic<Node*>) * (height - 1));
+  return new (node_memory) Node(key);
 }
 
-template<typename Key, class Comparator>
-inline SkipList<Key,Comparator>::Iterator::Iterator(const SkipList* list) {
+template <typename Key, class Comparator>
+inline SkipList<Key, Comparator>::Iterator::Iterator(const SkipList* list) {
   list_ = list;
-  node_ = NULL;
+  node_ = nullptr;
 }
 
-template<typename Key, class Comparator>
-inline bool SkipList<Key,Comparator>::Iterator::Valid() const {
-  return node_ != NULL;
+template <typename Key, class Comparator>
+inline bool SkipList<Key, Comparator>::Iterator::Valid() const {
+  return node_ != nullptr;
 }
 
-template<typename Key, class Comparator>
-inline const Key& SkipList<Key,Comparator>::Iterator::key() const {
+template <typename Key, class Comparator>
+inline const Key& SkipList<Key, Comparator>::Iterator::key() const {
   assert(Valid());
   return node_->key;
 }
 
-template<typename Key, class Comparator>
-inline void SkipList<Key,Comparator>::Iterator::Next() {
+template <typename Key, class Comparator>
+inline void SkipList<Key, Comparator>::Iterator::Next() {
   assert(Valid());
   node_ = node_->Next(0);
 }
 
-template<typename Key, class Comparator>
-inline void SkipList<Key,Comparator>::Iterator::Prev() {
+template <typename Key, class Comparator>
+inline void SkipList<Key, Comparator>::Iterator::Prev() {
   // Instead of using explicit "prev" links, we just search for the
   // last node that falls before key.
   assert(Valid());
   node_ = list_->FindLessThan(node_->key);
   if (node_ == list_->head_) {
-    node_ = NULL;
+    node_ = nullptr;
   }
 }
 
-template<typename Key, class Comparator>
-inline void SkipList<Key,Comparator>::Iterator::Seek(const Key& target) {
-  node_ = list_->FindGreaterOrEqual(target, NULL);
+template <typename Key, class Comparator>
+inline void SkipList<Key, Comparator>::Iterator::Seek(const Key& target) {
+  node_ = list_->FindGreaterOrEqual(target, nullptr);
 }
 
-template<typename Key, class Comparator>
-inline void SkipList<Key,Comparator>::Iterator::SeekToFirst() {
+template <typename Key, class Comparator>
+inline void SkipList<Key, Comparator>::Iterator::SeekToFirst() {
   node_ = list_->head_->Next(0);
 }
 
-template<typename Key, class Comparator>
-inline void SkipList<Key,Comparator>::Iterator::SeekToLast() {
+template <typename Key, class Comparator>
+inline void SkipList<Key, Comparator>::Iterator::SeekToLast() {
   node_ = list_->FindLast();
   if (node_ == list_->head_) {
-    node_ = NULL;
+    node_ = nullptr;
   }
 }
 
-template<typename Key, class Comparator>
-int SkipList<Key,Comparator>::RandomHeight() {
+template <typename Key, class Comparator>
+int SkipList<Key, Comparator>::RandomHeight() {
   // Increase height with probability 1 in kBranching
   static const unsigned int kBranching = 4;
   int height = 1;
@@ -252,15 +251,16 @@ int SkipList<Key,Comparator>::RandomHeight() {
   return height;
 }
 
-template<typename Key, class Comparator>
-bool SkipList<Key,Comparator>::KeyIsAfterNode(const Key& key, Node* n) const {
-  // NULL n is considered infinite
-  return (n != NULL) && (compare_(n->key, key) < 0);
+template <typename Key, class Comparator>
+bool SkipList<Key, Comparator>::KeyIsAfterNode(const Key& key, Node* n) const {
+  // null n is considered infinite
+  return (n != nullptr) && (compare_(n->key, key) < 0);
 }
 
-template<typename Key, class Comparator>
-typename SkipList<Key,Comparator>::Node* SkipList<Key,Comparator>::FindGreaterOrEqual(const Key& key, Node** prev)
-    const {
+template <typename Key, class Comparator>
+typename SkipList<Key, Comparator>::Node*
+SkipList<Key, Comparator>::FindGreaterOrEqual(const Key& key,
+                                              Node** prev) const {
   Node* x = head_;
   int level = GetMaxHeight() - 1;
   while (true) {
@@ -269,7 +269,7 @@ typename SkipList<Key,Comparator>::Node* SkipList<Key,Comparator>::FindGreaterOr
       // Keep searching in this list
       x = next;
     } else {
-      if (prev != NULL) prev[level] = x;
+      if (prev != nullptr) prev[level] = x;
       if (level == 0) {
         return next;
       } else {
@@ -280,15 +280,15 @@ typename SkipList<Key,Comparator>::Node* SkipList<Key,Comparator>::FindGreaterOr
   }
 }
 
-template<typename Key, class Comparator>
-typename SkipList<Key,Comparator>::Node*
-SkipList<Key,Comparator>::FindLessThan(const Key& key) const {
+template <typename Key, class Comparator>
+typename SkipList<Key, Comparator>::Node*
+SkipList<Key, Comparator>::FindLessThan(const Key& key) const {
   Node* x = head_;
   int level = GetMaxHeight() - 1;
   while (true) {
     assert(x == head_ || compare_(x->key, key) < 0);
     Node* next = x->Next(level);
-    if (next == NULL || compare_(next->key, key) >= 0) {
+    if (next == nullptr || compare_(next->key, key) >= 0) {
       if (level == 0) {
         return x;
       } else {
@@ -301,14 +301,14 @@ SkipList<Key,Comparator>::FindLessThan(const Key& key) const {
   }
 }
 
-template<typename Key, class Comparator>
-typename SkipList<Key,Comparator>::Node* SkipList<Key,Comparator>::FindLast()
+template <typename Key, class Comparator>
+typename SkipList<Key, Comparator>::Node* SkipList<Key, Comparator>::FindLast()
     const {
   Node* x = head_;
   int level = GetMaxHeight() - 1;
   while (true) {
     Node* next = x->Next(level);
-    if (next == NULL) {
+    if (next == nullptr) {
       if (level == 0) {
         return x;
       } else {
@@ -321,43 +321,41 @@ typename SkipList<Key,Comparator>::Node* SkipList<Key,Comparator>::FindLast()
   }
 }
 
-template<typename Key, class Comparator>
-SkipList<Key,Comparator>::SkipList(Comparator cmp, Arena* arena)
+template <typename Key, class Comparator>
+SkipList<Key, Comparator>::SkipList(Comparator cmp, Arena* arena)
     : compare_(cmp),
       arena_(arena),
       head_(NewNode(0 /* any key will do */, kMaxHeight)),
-      max_height_(reinterpret_cast<void*>(1)),
+      max_height_(1),
       rnd_(0xdeadbeef) {
   for (int i = 0; i < kMaxHeight; i++) {
-    head_->SetNext(i, NULL);
+    head_->SetNext(i, nullptr);
   }
 }
 
-template<typename Key, class Comparator>
-void SkipList<Key,Comparator>::Insert(const Key& key) {
+template <typename Key, class Comparator>
+void SkipList<Key, Comparator>::Insert(const Key& key) {
   // TODO(opt): We can use a barrier-free variant of FindGreaterOrEqual()
   // here since Insert() is externally synchronized.
   Node* prev[kMaxHeight];
   Node* x = FindGreaterOrEqual(key, prev);
 
   // Our data structure does not allow duplicate insertion
-  assert(x == NULL || !Equal(key, x->key));
+  assert(x == nullptr || !Equal(key, x->key));
 
   int height = RandomHeight();
   if (height > GetMaxHeight()) {
     for (int i = GetMaxHeight(); i < height; i++) {
       prev[i] = head_;
     }
-    //fprintf(stderr, "Change height from %d to %d\n", max_height_, height);
-
     // It is ok to mutate max_height_ without any synchronization
     // with concurrent readers.  A concurrent reader that observes
     // the new value of max_height_ will see either the old value of
-    // new level pointers from head_ (NULL), or a new value set in
+    // new level pointers from head_ (nullptr), or a new value set in
     // the loop below.  In the former case the reader will
-    // immediately drop to the next level since NULL sorts after all
+    // immediately drop to the next level since nullptr sorts after all
     // keys.  In the latter case the reader will use the new node.
-    max_height_.NoBarrier_Store(reinterpret_cast<void*>(height));
+    max_height_.store(height, std::memory_order_relaxed);
   }
 
   x = NewNode(key, height);
@@ -369,10 +367,10 @@ void SkipList<Key,Comparator>::Insert(const Key& key) {
   }
 }
 
-template<typename Key, class Comparator>
-bool SkipList<Key,Comparator>::Contains(const Key& key) const {
-  Node* x = FindGreaterOrEqual(key, NULL);
-  if (x != NULL && Equal(key, x->key)) {
+template <typename Key, class Comparator>
+bool SkipList<Key, Comparator>::Contains(const Key& key) const {
+  Node* x = FindGreaterOrEqual(key, nullptr);
+  if (x != nullptr && Equal(key, x->key)) {
     return true;
   } else {
     return false;
diff --git a/db/skiplist_test.cc b/db/skiplist_test.cc
index c78f4b4..9fa2d96 100644
--- a/db/skiplist_test.cc
+++ b/db/skiplist_test.cc
@@ -3,8 +3,13 @@
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
 #include "db/skiplist.h"
+
+#include <atomic>
 #include <set>
+
 #include "leveldb/env.h"
+#include "port/port.h"
+#include "port/thread_annotations.h"
 #include "util/arena.h"
 #include "util/hash.h"
 #include "util/random.h"
@@ -26,7 +31,7 @@ struct Comparator {
   }
 };
 
-class SkipTest { };
+class SkipTest {};
 
 TEST(SkipTest, Empty) {
   Arena arena;
@@ -112,8 +117,7 @@ TEST(SkipTest, InsertAndLookup) {
 
     // Compare against model iterator
     for (std::set<Key>::reverse_iterator model_iter = keys.rbegin();
-         model_iter != keys.rend();
-         ++model_iter) {
+         model_iter != keys.rend(); ++model_iter) {
       ASSERT_TRUE(iter.Valid());
       ASSERT_EQ(*model_iter, iter.key());
       iter.Prev();
@@ -126,7 +130,7 @@ TEST(SkipTest, InsertAndLookup) {
 // concurrent readers (with no synchronization other than when a
 // reader's iterator is created), the reader always observes all the
 // data that was present in the skip list when the iterator was
-// constructor.  Because insertions are happening concurrently, we may
+// constructed.  Because insertions are happening concurrently, we may
 // also observe new values that were inserted since the iterator was
 // constructed, but we should never miss any values that were present
 // at iterator construction time.
@@ -155,12 +159,12 @@ class ConcurrentTest {
   static uint64_t hash(Key key) { return key & 0xff; }
 
   static uint64_t HashNumbers(uint64_t k, uint64_t g) {
-    uint64_t data[2] = { k, g };
+    uint64_t data[2] = {k, g};
     return Hash(reinterpret_cast<char*>(data), sizeof(data), 0);
   }
 
   static Key MakeKey(uint64_t k, uint64_t g) {
-    assert(sizeof(Key) == sizeof(uint64_t));
+    static_assert(sizeof(Key) == sizeof(uint64_t), "");
     assert(k <= K);  // We sometimes pass K to seek to the end of the skiplist
     assert(g <= 0xffffffffu);
     return ((k << 40) | (g << 8) | (HashNumbers(k, g) & 0xff));
@@ -186,13 +190,11 @@ class ConcurrentTest {
 
   // Per-key generation
   struct State {
-    port::AtomicPointer generation[K];
-    void Set(int k, intptr_t v) {
-      generation[k].Release_Store(reinterpret_cast<void*>(v));
-    }
-    intptr_t Get(int k) {
-      return reinterpret_cast<intptr_t>(generation[k].Acquire_Load());
+    std::atomic<int> generation[K];
+    void Set(int k, int v) {
+      generation[k].store(v, std::memory_order_release);
     }
+    int Get(int k) { return generation[k].load(std::memory_order_acquire); }
 
     State() {
       for (int k = 0; k < K; k++) {
@@ -211,7 +213,7 @@ class ConcurrentTest {
   SkipList<Key, Comparator> list_;
 
  public:
-  ConcurrentTest() : list_(Comparator(), &arena_) { }
+  ConcurrentTest() : list_(Comparator(), &arena_) {}
 
   // REQUIRES: External synchronization
   void WriteStep(Random* rnd) {
@@ -250,11 +252,9 @@ class ConcurrentTest {
         // Note that generation 0 is never inserted, so it is ok if
         // <*,0,*> is missing.
         ASSERT_TRUE((gen(pos) == 0) ||
-                    (gen(pos) > initial_state.Get(key(pos)))
-                    ) << "key: " << key(pos)
-                      << "; gen: " << gen(pos)
-                      << "; initgen: "
-                      << initial_state.Get(key(pos));
+                    (gen(pos) > static_cast<Key>(initial_state.Get(key(pos)))))
+            << "key: " << key(pos) << "; gen: " << gen(pos)
+            << "; initgen: " << initial_state.Get(key(pos));
 
         // Advance to next key in the valid key space
         if (key(pos) < key(current)) {
@@ -298,21 +298,14 @@ class TestState {
  public:
   ConcurrentTest t_;
   int seed_;
-  port::AtomicPointer quit_flag_;
+  std::atomic<bool> quit_flag_;
 
-  enum ReaderState {
-    STARTING,
-    RUNNING,
-    DONE
-  };
+  enum ReaderState { STARTING, RUNNING, DONE };
 
   explicit TestState(int s)
-      : seed_(s),
-        quit_flag_(NULL),
-        state_(STARTING),
-        state_cv_(&mu_) {}
+      : seed_(s), quit_flag_(false), state_(STARTING), state_cv_(&mu_) {}
 
-  void Wait(ReaderState s) {
+  void Wait(ReaderState s) LOCKS_EXCLUDED(mu_) {
     mu_.Lock();
     while (state_ != s) {
       state_cv_.Wait();
@@ -320,7 +313,7 @@ class TestState {
     mu_.Unlock();
   }
 
-  void Change(ReaderState s) {
+  void Change(ReaderState s) LOCKS_EXCLUDED(mu_) {
     mu_.Lock();
     state_ = s;
     state_cv_.Signal();
@@ -329,8 +322,8 @@ class TestState {
 
  private:
   port::Mutex mu_;
-  ReaderState state_;
-  port::CondVar state_cv_;
+  ReaderState state_ GUARDED_BY(mu_);
+  port::CondVar state_cv_ GUARDED_BY(mu_);
 };
 
 static void ConcurrentReader(void* arg) {
@@ -338,7 +331,7 @@ static void ConcurrentReader(void* arg) {
   Random rnd(state->seed_);
   int64_t reads = 0;
   state->Change(TestState::RUNNING);
-  while (!state->quit_flag_.Acquire_Load()) {
+  while (!state->quit_flag_.load(std::memory_order_acquire)) {
     state->t_.ReadStep(&rnd);
     ++reads;
   }
@@ -360,7 +353,7 @@ static void RunConcurrent(int run) {
     for (int i = 0; i < kSize; i++) {
       state.t_.WriteStep(&rnd);
     }
-    state.quit_flag_.Release_Store(&state);  // Any non-NULL arg will do
+    state.quit_flag_.store(true, std::memory_order_release);
     state.Wait(TestState::DONE);
   }
 }
@@ -373,6 +366,4 @@ TEST(SkipTest, Concurrent5) { RunConcurrent(5); }
 
 }  // namespace leveldb
 
-int main(int argc, char** argv) {
-  return leveldb::test::RunAllTests();
-}
+int main(int argc, char** argv) { return leveldb::test::RunAllTests(); }
diff --git a/db/snapshot.h b/db/snapshot.h
index 6ed413c..9f1d664 100644
--- a/db/snapshot.h
+++ b/db/snapshot.h
@@ -16,50 +16,78 @@ class SnapshotList;
 // Each SnapshotImpl corresponds to a particular sequence number.
 class SnapshotImpl : public Snapshot {
  public:
-  SequenceNumber number_;  // const after creation
+  SnapshotImpl(SequenceNumber sequence_number)
+      : sequence_number_(sequence_number) {}
+
+  SequenceNumber sequence_number() const { return sequence_number_; }
 
  private:
   friend class SnapshotList;
 
-  // SnapshotImpl is kept in a doubly-linked circular list
+  // SnapshotImpl is kept in a doubly-linked circular list. The SnapshotList
+  // implementation operates on the next/previous fields direcly.
   SnapshotImpl* prev_;
   SnapshotImpl* next_;
 
-  SnapshotList* list_;                 // just for sanity checks
+  const SequenceNumber sequence_number_;
+
+#if !defined(NDEBUG)
+  SnapshotList* list_ = nullptr;
+#endif  // !defined(NDEBUG)
 };
 
 class SnapshotList {
  public:
-  SnapshotList() {
-    list_.prev_ = &list_;
-    list_.next_ = &list_;
+  SnapshotList() : head_(0) {
+    head_.prev_ = &head_;
+    head_.next_ = &head_;
+  }
+
+  bool empty() const { return head_.next_ == &head_; }
+  SnapshotImpl* oldest() const {
+    assert(!empty());
+    return head_.next_;
   }
+  SnapshotImpl* newest() const {
+    assert(!empty());
+    return head_.prev_;
+  }
+
+  // Creates a SnapshotImpl and appends it to the end of the list.
+  SnapshotImpl* New(SequenceNumber sequence_number) {
+    assert(empty() || newest()->sequence_number_ <= sequence_number);
+
+    SnapshotImpl* snapshot = new SnapshotImpl(sequence_number);
 
-  bool empty() const { return list_.next_ == &list_; }
-  SnapshotImpl* oldest() const { assert(!empty()); return list_.next_; }
-  SnapshotImpl* newest() const { assert(!empty()); return list_.prev_; }
-
-  const SnapshotImpl* New(SequenceNumber seq) {
-    SnapshotImpl* s = new SnapshotImpl;
-    s->number_ = seq;
-    s->list_ = this;
-    s->next_ = &list_;
-    s->prev_ = list_.prev_;
-    s->prev_->next_ = s;
-    s->next_->prev_ = s;
-    return s;
+#if !defined(NDEBUG)
+    snapshot->list_ = this;
+#endif  // !defined(NDEBUG)
+    snapshot->next_ = &head_;
+    snapshot->prev_ = head_.prev_;
+    snapshot->prev_->next_ = snapshot;
+    snapshot->next_->prev_ = snapshot;
+    return snapshot;
   }
 
-  void Delete(const SnapshotImpl* s) {
-    assert(s->list_ == this);
-    s->prev_->next_ = s->next_;
-    s->next_->prev_ = s->prev_;
-    delete s;
+  // Removes a SnapshotImpl from this list.
+  //
+  // The snapshot must have been created by calling New() on this list.
+  //
+  // The snapshot pointer should not be const, because its memory is
+  // deallocated. However, that would force us to change DB::ReleaseSnapshot(),
+  // which is in the API, and currently takes a const Snapshot.
+  void Delete(const SnapshotImpl* snapshot) {
+#if !defined(NDEBUG)
+    assert(snapshot->list_ == this);
+#endif  // !defined(NDEBUG)
+    snapshot->prev_->next_ = snapshot->next_;
+    snapshot->next_->prev_ = snapshot->prev_;
+    delete snapshot;
   }
 
  private:
   // Dummy head of doubly-linked list of snapshots
-  SnapshotImpl list_;
+  SnapshotImpl head_;
 };
 
 }  // namespace leveldb
diff --git a/db/table_cache.cc b/db/table_cache.cc
index e3d82cd..73f05fd 100644
--- a/db/table_cache.cc
+++ b/db/table_cache.cc
@@ -29,18 +29,14 @@ static void UnrefEntry(void* arg1, void* arg2) {
   cache->Release(h);
 }
 
-TableCache::TableCache(const std::string& dbname,
-                       const Options* options,
+TableCache::TableCache(const std::string& dbname, const Options& options,
                        int entries)
-    : env_(options->env),
+    : env_(options.env),
       dbname_(dbname),
       options_(options),
-      cache_(NewLRUCache(entries)) {
-}
+      cache_(NewLRUCache(entries)) {}
 
-TableCache::~TableCache() {
-  delete cache_;
-}
+TableCache::~TableCache() { delete cache_; }
 
 Status TableCache::FindTable(uint64_t file_number, uint64_t file_size,
                              Cache::Handle** handle) {
@@ -49,10 +45,10 @@ Status TableCache::FindTable(uint64_t file_number, uint64_t file_size,
   EncodeFixed64(buf, file_number);
   Slice key(buf, sizeof(buf));
   *handle = cache_->Lookup(key);
-  if (*handle == NULL) {
+  if (*handle == nullptr) {
     std::string fname = TableFileName(dbname_, file_number);
-    RandomAccessFile* file = NULL;
-    Table* table = NULL;
+    RandomAccessFile* file = nullptr;
+    Table* table = nullptr;
     s = env_->NewRandomAccessFile(fname, &file);
     if (!s.ok()) {
       std::string old_fname = SSTTableFileName(dbname_, file_number);
@@ -61,11 +57,11 @@ Status TableCache::FindTable(uint64_t file_number, uint64_t file_size,
       }
     }
     if (s.ok()) {
-      s = Table::Open(*options_, file, file_size, &table);
+      s = Table::Open(options_, file, file_size, &table);
     }
 
     if (!s.ok()) {
-      assert(table == NULL);
+      assert(table == nullptr);
       delete file;
       // We do not cache error results so that if the error is transient,
       // or somebody repairs the file, we recover automatically.
@@ -80,14 +76,13 @@ Status TableCache::FindTable(uint64_t file_number, uint64_t file_size,
 }
 
 Iterator* TableCache::NewIterator(const ReadOptions& options,
-                                  uint64_t file_number,
-                                  uint64_t file_size,
+                                  uint64_t file_number, uint64_t file_size,
                                   Table** tableptr) {
-  if (tableptr != NULL) {
-    *tableptr = NULL;
+  if (tableptr != nullptr) {
+    *tableptr = nullptr;
   }
 
-  Cache::Handle* handle = NULL;
+  Cache::Handle* handle = nullptr;
   Status s = FindTable(file_number, file_size, &handle);
   if (!s.ok()) {
     return NewErrorIterator(s);
@@ -96,23 +91,21 @@ Iterator* TableCache::NewIterator(const ReadOptions& options,
   Table* table = reinterpret_cast<TableAndFile*>(cache_->Value(handle))->table;
   Iterator* result = table->NewIterator(options);
   result->RegisterCleanup(&UnrefEntry, cache_, handle);
-  if (tableptr != NULL) {
+  if (tableptr != nullptr) {
     *tableptr = table;
   }
   return result;
 }
 
-Status TableCache::Get(const ReadOptions& options,
-                       uint64_t file_number,
-                       uint64_t file_size,
-                       const Slice& k,
-                       void* arg,
-                       void (*saver)(void*, const Slice&, const Slice&)) {
-  Cache::Handle* handle = NULL;
+Status TableCache::Get(const ReadOptions& options, uint64_t file_number,
+                       uint64_t file_size, const Slice& k, void* arg,
+                       void (*handle_result)(void*, const Slice&,
+                                             const Slice&)) {
+  Cache::Handle* handle = nullptr;
   Status s = FindTable(file_number, file_size, &handle);
   if (s.ok()) {
     Table* t = reinterpret_cast<TableAndFile*>(cache_->Value(handle))->table;
-    s = t->InternalGet(options, k, arg, saver);
+    s = t->InternalGet(options, k, arg, handle_result);
     cache_->Release(handle);
   }
   return s;
diff --git a/db/table_cache.h b/db/table_cache.h
index 8cf4aaf..93069c8 100644
--- a/db/table_cache.h
+++ b/db/table_cache.h
@@ -7,8 +7,10 @@
 #ifndef STORAGE_LEVELDB_DB_TABLE_CACHE_H_
 #define STORAGE_LEVELDB_DB_TABLE_CACHE_H_
 
-#include <string>
 #include <stdint.h>
+
+#include <string>
+
 #include "db/dbformat.h"
 #include "leveldb/cache.h"
 #include "leveldb/table.h"
@@ -20,40 +22,35 @@ class Env;
 
 class TableCache {
  public:
-  TableCache(const std::string& dbname, const Options* options, int entries);
+  TableCache(const std::string& dbname, const Options& options, int entries);
   ~TableCache();
 
   // Return an iterator for the specified file number (the corresponding
   // file length must be exactly "file_size" bytes).  If "tableptr" is
-  // non-NULL, also sets "*tableptr" to point to the Table object
-  // underlying the returned iterator, or NULL if no Table object underlies
-  // the returned iterator.  The returned "*tableptr" object is owned by
-  // the cache and should not be deleted, and is valid for as long as the
+  // non-null, also sets "*tableptr" to point to the Table object
+  // underlying the returned iterator, or to nullptr if no Table object
+  // underlies the returned iterator.  The returned "*tableptr" object is owned
+  // by the cache and should not be deleted, and is valid for as long as the
   // returned iterator is live.
-  Iterator* NewIterator(const ReadOptions& options,
-                        uint64_t file_number,
-                        uint64_t file_size,
-                        Table** tableptr = NULL);
+  Iterator* NewIterator(const ReadOptions& options, uint64_t file_number,
+                        uint64_t file_size, Table** tableptr = nullptr);
 
   // If a seek to internal key "k" in specified file finds an entry,
   // call (*handle_result)(arg, found_key, found_value).
-  Status Get(const ReadOptions& options,
-             uint64_t file_number,
-             uint64_t file_size,
-             const Slice& k,
-             void* arg,
+  Status Get(const ReadOptions& options, uint64_t file_number,
+             uint64_t file_size, const Slice& k, void* arg,
              void (*handle_result)(void*, const Slice&, const Slice&));
 
   // Evict any entry for the specified file number
   void Evict(uint64_t file_number);
 
  private:
+  Status FindTable(uint64_t file_number, uint64_t file_size, Cache::Handle**);
+
   Env* const env_;
   const std::string dbname_;
-  const Options* options_;
+  const Options& options_;
   Cache* cache_;
-
-  Status FindTable(uint64_t file_number, uint64_t file_size, Cache::Handle**);
 };
 
 }  // namespace leveldb
diff --git a/db/version_edit.cc b/db/version_edit.cc
index f10a2d5..cd770ef 100644
--- a/db/version_edit.cc
+++ b/db/version_edit.cc
@@ -12,15 +12,15 @@ namespace leveldb {
 // Tag numbers for serialized VersionEdit.  These numbers are written to
 // disk and should not be changed.
 enum Tag {
-  kComparator           = 1,
-  kLogNumber            = 2,
-  kNextFileNumber       = 3,
-  kLastSequence         = 4,
-  kCompactPointer       = 5,
-  kDeletedFile          = 6,
-  kNewFile              = 7,
+  kComparator = 1,
+  kLogNumber = 2,
+  kNextFileNumber = 3,
+  kLastSequence = 4,
+  kCompactPointer = 5,
+  kDeletedFile = 6,
+  kNewFile = 7,
   // 8 was used for large value refs
-  kPrevLogNumber        = 9
+  kPrevLogNumber = 9
 };
 
 void VersionEdit::Clear() {
@@ -66,12 +66,10 @@ void VersionEdit::EncodeTo(std::string* dst) const {
     PutLengthPrefixedSlice(dst, compact_pointers_[i].second.Encode());
   }
 
-  for (DeletedFileSet::const_iterator iter = deleted_files_.begin();
-       iter != deleted_files_.end();
-       ++iter) {
+  for (const auto& deleted_file_kvp : deleted_files_) {
     PutVarint32(dst, kDeletedFile);
-    PutVarint32(dst, iter->first);   // level
-    PutVarint64(dst, iter->second);  // file number
+    PutVarint32(dst, deleted_file_kvp.first);   // level
+    PutVarint64(dst, deleted_file_kvp.second);  // file number
   }
 
   for (size_t i = 0; i < new_files_.size(); i++) {
@@ -88,8 +86,7 @@ void VersionEdit::EncodeTo(std::string* dst) const {
 static bool GetInternalKey(Slice* input, InternalKey* dst) {
   Slice str;
   if (GetLengthPrefixedSlice(input, &str)) {
-    dst->DecodeFrom(str);
-    return true;
+    return dst->DecodeFrom(str);
   } else {
     return false;
   }
@@ -97,8 +94,7 @@ static bool GetInternalKey(Slice* input, InternalKey* dst) {
 
 static bool GetLevel(Slice* input, int* level) {
   uint32_t v;
-  if (GetVarint32(input, &v) &&
-      v < config::kNumLevels) {
+  if (GetVarint32(input, &v) && v < config::kNumLevels) {
     *level = v;
     return true;
   } else {
@@ -109,7 +105,7 @@ static bool GetLevel(Slice* input, int* level) {
 Status VersionEdit::DecodeFrom(const Slice& src) {
   Clear();
   Slice input = src;
-  const char* msg = NULL;
+  const char* msg = nullptr;
   uint32_t tag;
 
   // Temporary storage for parsing
@@ -119,7 +115,7 @@ Status VersionEdit::DecodeFrom(const Slice& src) {
   Slice str;
   InternalKey key;
 
-  while (msg == NULL && GetVarint32(&input, &tag)) {
+  while (msg == nullptr && GetVarint32(&input, &tag)) {
     switch (tag) {
       case kComparator:
         if (GetLengthPrefixedSlice(&input, &str)) {
@@ -163,8 +159,7 @@ Status VersionEdit::DecodeFrom(const Slice& src) {
         break;
 
       case kCompactPointer:
-        if (GetLevel(&input, &level) &&
-            GetInternalKey(&input, &key)) {
+        if (GetLevel(&input, &level) && GetInternalKey(&input, &key)) {
           compact_pointers_.push_back(std::make_pair(level, key));
         } else {
           msg = "compaction pointer";
@@ -172,8 +167,7 @@ Status VersionEdit::DecodeFrom(const Slice& src) {
         break;
 
       case kDeletedFile:
-        if (GetLevel(&input, &level) &&
-            GetVarint64(&input, &number)) {
+        if (GetLevel(&input, &level) && GetVarint64(&input, &number)) {
           deleted_files_.insert(std::make_pair(level, number));
         } else {
           msg = "deleted file";
@@ -181,8 +175,7 @@ Status VersionEdit::DecodeFrom(const Slice& src) {
         break;
 
       case kNewFile:
-        if (GetLevel(&input, &level) &&
-            GetVarint64(&input, &f.number) &&
+        if (GetLevel(&input, &level) && GetVarint64(&input, &f.number) &&
             GetVarint64(&input, &f.file_size) &&
             GetInternalKey(&input, &f.smallest) &&
             GetInternalKey(&input, &f.largest)) {
@@ -198,12 +191,12 @@ Status VersionEdit::DecodeFrom(const Slice& src) {
     }
   }
 
-  if (msg == NULL && !input.empty()) {
+  if (msg == nullptr && !input.empty()) {
     msg = "invalid tag";
   }
 
   Status result;
-  if (msg != NULL) {
+  if (msg != nullptr) {
     result = Status::Corruption("VersionEdit", msg);
   }
   return result;
@@ -238,13 +231,11 @@ std::string VersionEdit::DebugString() const {
     r.append(" ");
     r.append(compact_pointers_[i].second.DebugString());
   }
-  for (DeletedFileSet::const_iterator iter = deleted_files_.begin();
-       iter != deleted_files_.end();
-       ++iter) {
+  for (const auto& deleted_files_kvp : deleted_files_) {
     r.append("\n  DeleteFile: ");
-    AppendNumberTo(&r, iter->first);
+    AppendNumberTo(&r, deleted_files_kvp.first);
     r.append(" ");
-    AppendNumberTo(&r, iter->second);
+    AppendNumberTo(&r, deleted_files_kvp.second);
   }
   for (size_t i = 0; i < new_files_.size(); i++) {
     const FileMetaData& f = new_files_[i].second;
diff --git a/db/version_edit.h b/db/version_edit.h
index eaef77b..86b2f22 100644
--- a/db/version_edit.h
+++ b/db/version_edit.h
@@ -8,6 +8,7 @@
 #include <set>
 #include <utility>
 #include <vector>
+
 #include "db/dbformat.h"
 
 namespace leveldb {
@@ -15,20 +16,20 @@ namespace leveldb {
 class VersionSet;
 
 struct FileMetaData {
+  FileMetaData() : refs(0), allowed_seeks(1 << 30), file_size(0) {}
+
   int refs;
-  int allowed_seeks;          // Seeks allowed until compaction
+  int allowed_seeks;  // Seeks allowed until compaction
   uint64_t number;
-  uint64_t file_size;         // File size in bytes
-  InternalKey smallest;       // Smallest internal key served by table
-  InternalKey largest;        // Largest internal key served by table
-
-  FileMetaData() : refs(0), allowed_seeks(1 << 30), file_size(0) { }
+  uint64_t file_size;    // File size in bytes
+  InternalKey smallest;  // Smallest internal key served by table
+  InternalKey largest;   // Largest internal key served by table
 };
 
 class VersionEdit {
  public:
   VersionEdit() { Clear(); }
-  ~VersionEdit() { }
+  ~VersionEdit() = default;
 
   void Clear();
 
@@ -59,10 +60,8 @@ class VersionEdit {
   // Add the specified file at the specified number.
   // REQUIRES: This version has not been saved (see VersionSet::SaveTo)
   // REQUIRES: "smallest" and "largest" are smallest and largest keys in file
-  void AddFile(int level, uint64_t file,
-               uint64_t file_size,
-               const InternalKey& smallest,
-               const InternalKey& largest) {
+  void AddFile(int level, uint64_t file, uint64_t file_size,
+               const InternalKey& smallest, const InternalKey& largest) {
     FileMetaData f;
     f.number = file;
     f.file_size = file_size;
@@ -84,7 +83,7 @@ class VersionEdit {
  private:
   friend class VersionSet;
 
-  typedef std::set< std::pair<int, uint64_t> > DeletedFileSet;
+  typedef std::set<std::pair<int, uint64_t> > DeletedFileSet;
 
   std::string comparator_;
   uint64_t log_number_;
@@ -97,9 +96,9 @@ class VersionEdit {
   bool has_next_file_number_;
   bool has_last_sequence_;
 
-  std::vector< std::pair<int, InternalKey> > compact_pointers_;
+  std::vector<std::pair<int, InternalKey> > compact_pointers_;
   DeletedFileSet deleted_files_;
-  std::vector< std::pair<int, FileMetaData> > new_files_;
+  std::vector<std::pair<int, FileMetaData> > new_files_;
 };
 
 }  // namespace leveldb
diff --git a/db/version_edit_test.cc b/db/version_edit_test.cc
index 280310b..0b7cda8 100644
--- a/db/version_edit_test.cc
+++ b/db/version_edit_test.cc
@@ -17,7 +17,7 @@ static void TestEncodeDecode(const VersionEdit& edit) {
   ASSERT_EQ(encoded, encoded2);
 }
 
-class VersionEditTest { };
+class VersionEditTest {};
 
 TEST(VersionEditTest, EncodeDecode) {
   static const uint64_t kBig = 1ull << 50;
@@ -41,6 +41,4 @@ TEST(VersionEditTest, EncodeDecode) {
 
 }  // namespace leveldb
 
-int main(int argc, char** argv) {
-  return leveldb::test::RunAllTests();
-}
+int main(int argc, char** argv) { return leveldb::test::RunAllTests(); }
diff --git a/db/version_set.cc b/db/version_set.cc
index aa83df5..b62a2d0 100644
--- a/db/version_set.cc
+++ b/db/version_set.cc
@@ -4,8 +4,10 @@
 
 #include "db/version_set.h"
 
-#include <algorithm>
 #include <stdio.h>
+
+#include <algorithm>
+
 #include "db/filename.h"
 #include "db/log_reader.h"
 #include "db/log_writer.h"
@@ -20,21 +22,29 @@
 
 namespace leveldb {
 
-static const int kTargetFileSize = 2 * 1048576;
+static size_t TargetFileSize(const Options* options) {
+  return options->max_file_size;
+}
 
 // Maximum bytes of overlaps in grandparent (i.e., level+2) before we
 // stop building a single file in a level->level+1 compaction.
-static const int64_t kMaxGrandParentOverlapBytes = 10 * kTargetFileSize;
+static int64_t MaxGrandParentOverlapBytes(const Options* options) {
+  return 10 * TargetFileSize(options);
+}
 
 // Maximum number of bytes in all compacted files.  We avoid expanding
 // the lower level file set of a compaction if it would make the
 // total compaction cover more than this many bytes.
-static const int64_t kExpandedCompactionByteSizeLimit = 25 * kTargetFileSize;
+static int64_t ExpandedCompactionByteSizeLimit(const Options* options) {
+  return 25 * TargetFileSize(options);
+}
 
-static double MaxBytesForLevel(int level) {
+static double MaxBytesForLevel(const Options* options, int level) {
   // Note: the result for level zero is not really used since we set
   // the level-0 compaction threshold based on number of files.
-  double result = 10 * 1048576.0;  // Result for both level-0 and level-1
+
+  // Result for both level-0 and level-1
+  double result = 10. * 1048576.0;
   while (level > 1) {
     result *= 10;
     level--;
@@ -42,8 +52,9 @@ static double MaxBytesForLevel(int level) {
   return result;
 }
 
-static uint64_t MaxFileSizeForLevel(int level) {
-  return kTargetFileSize;  // We could vary per level to reduce number of files?
+static uint64_t MaxFileSizeForLevel(const Options* options, int level) {
+  // We could vary per level to reduce number of files?
+  return TargetFileSize(options);
 }
 
 static int64_t TotalFileSize(const std::vector<FileMetaData*>& files) {
@@ -75,8 +86,7 @@ Version::~Version() {
 }
 
 int FindFile(const InternalKeyComparator& icmp,
-             const std::vector<FileMetaData*>& files,
-             const Slice& key) {
+             const std::vector<FileMetaData*>& files, const Slice& key) {
   uint32_t left = 0;
   uint32_t right = files.size();
   while (left < right) {
@@ -95,26 +105,25 @@ int FindFile(const InternalKeyComparator& icmp,
   return right;
 }
 
-static bool AfterFile(const Comparator* ucmp,
-                      const Slice* user_key, const FileMetaData* f) {
-  // NULL user_key occurs before all keys and is therefore never after *f
-  return (user_key != NULL &&
+static bool AfterFile(const Comparator* ucmp, const Slice* user_key,
+                      const FileMetaData* f) {
+  // null user_key occurs before all keys and is therefore never after *f
+  return (user_key != nullptr &&
           ucmp->Compare(*user_key, f->largest.user_key()) > 0);
 }
 
-static bool BeforeFile(const Comparator* ucmp,
-                       const Slice* user_key, const FileMetaData* f) {
-  // NULL user_key occurs after all keys and is therefore never before *f
-  return (user_key != NULL &&
+static bool BeforeFile(const Comparator* ucmp, const Slice* user_key,
+                       const FileMetaData* f) {
+  // null user_key occurs after all keys and is therefore never before *f
+  return (user_key != nullptr &&
           ucmp->Compare(*user_key, f->smallest.user_key()) < 0);
 }
 
-bool SomeFileOverlapsRange(
-    const InternalKeyComparator& icmp,
-    bool disjoint_sorted_files,
-    const std::vector<FileMetaData*>& files,
-    const Slice* smallest_user_key,
-    const Slice* largest_user_key) {
+bool SomeFileOverlapsRange(const InternalKeyComparator& icmp,
+                           bool disjoint_sorted_files,
+                           const std::vector<FileMetaData*>& files,
+                           const Slice* smallest_user_key,
+                           const Slice* largest_user_key) {
   const Comparator* ucmp = icmp.user_comparator();
   if (!disjoint_sorted_files) {
     // Need to check against all files
@@ -132,10 +141,11 @@ bool SomeFileOverlapsRange(
 
   // Binary search over file list
   uint32_t index = 0;
-  if (smallest_user_key != NULL) {
+  if (smallest_user_key != nullptr) {
     // Find the earliest possible internal key for smallest_user_key
-    InternalKey small(*smallest_user_key, kMaxSequenceNumber,kValueTypeForSeek);
-    index = FindFile(icmp, files, small.Encode());
+    InternalKey small_key(*smallest_user_key, kMaxSequenceNumber,
+                          kValueTypeForSeek);
+    index = FindFile(icmp, files, small_key.Encode());
   }
 
   if (index >= files.size()) {
@@ -155,25 +165,21 @@ class Version::LevelFileNumIterator : public Iterator {
  public:
   LevelFileNumIterator(const InternalKeyComparator& icmp,
                        const std::vector<FileMetaData*>* flist)
-      : icmp_(icmp),
-        flist_(flist),
-        index_(flist->size()) {        // Marks as invalid
-  }
-  virtual bool Valid() const {
-    return index_ < flist_->size();
+      : icmp_(icmp), flist_(flist), index_(flist->size()) {  // Marks as invalid
   }
-  virtual void Seek(const Slice& target) {
+  bool Valid() const override { return index_ < flist_->size(); }
+  void Seek(const Slice& target) override {
     index_ = FindFile(icmp_, *flist_, target);
   }
-  virtual void SeekToFirst() { index_ = 0; }
-  virtual void SeekToLast() {
+  void SeekToFirst() override { index_ = 0; }
+  void SeekToLast() override {
     index_ = flist_->empty() ? 0 : flist_->size() - 1;
   }
-  virtual void Next() {
+  void Next() override {
     assert(Valid());
     index_++;
   }
-  virtual void Prev() {
+  void Prev() override {
     assert(Valid());
     if (index_ == 0) {
       index_ = flist_->size();  // Marks as invalid
@@ -181,17 +187,18 @@ class Version::LevelFileNumIterator : public Iterator {
       index_--;
     }
   }
-  Slice key() const {
+  Slice key() const override {
     assert(Valid());
     return (*flist_)[index_]->largest.Encode();
   }
-  Slice value() const {
+  Slice value() const override {
     assert(Valid());
     EncodeFixed64(value_buf_, (*flist_)[index_]->number);
-    EncodeFixed64(value_buf_+8, (*flist_)[index_]->file_size);
+    EncodeFixed64(value_buf_ + 8, (*flist_)[index_]->file_size);
     return Slice(value_buf_, sizeof(value_buf_));
   }
-  virtual Status status() const { return Status::OK(); }
+  Status status() const override { return Status::OK(); }
+
  private:
   const InternalKeyComparator icmp_;
   const std::vector<FileMetaData*>* const flist_;
@@ -201,16 +208,14 @@ class Version::LevelFileNumIterator : public Iterator {
   mutable char value_buf_[16];
 };
 
-static Iterator* GetFileIterator(void* arg,
-                                 const ReadOptions& options,
+static Iterator* GetFileIterator(void* arg, const ReadOptions& options,
                                  const Slice& file_value) {
   TableCache* cache = reinterpret_cast<TableCache*>(arg);
   if (file_value.size() != 16) {
     return NewErrorIterator(
         Status::Corruption("FileReader invoked with unexpected value"));
   } else {
-    return cache->NewIterator(options,
-                              DecodeFixed64(file_value.data()),
+    return cache->NewIterator(options, DecodeFixed64(file_value.data()),
                               DecodeFixed64(file_value.data() + 8));
   }
 }
@@ -218,17 +223,16 @@ static Iterator* GetFileIterator(void* arg,
 Iterator* Version::NewConcatenatingIterator(const ReadOptions& options,
                                             int level) const {
   return NewTwoLevelIterator(
-      new LevelFileNumIterator(vset_->icmp_, &files_[level]),
-      &GetFileIterator, vset_->table_cache_, options);
+      new LevelFileNumIterator(vset_->icmp_, &files_[level]), &GetFileIterator,
+      vset_->table_cache_, options);
 }
 
 void Version::AddIterators(const ReadOptions& options,
                            std::vector<Iterator*>* iters) {
   // Merge all level zero files together since they may overlap
   for (size_t i = 0; i < files_[0].size(); i++) {
-    iters->push_back(
-        vset_->table_cache_->NewIterator(
-            options, files_[0][i]->number, files_[0][i]->file_size));
+    iters->push_back(vset_->table_cache_->NewIterator(
+        options, files_[0][i]->number, files_[0][i]->file_size));
   }
 
   // For levels > 0, we can use a concatenating iterator that sequentially
@@ -255,7 +259,7 @@ struct Saver {
   Slice user_key;
   std::string* value;
 };
-}
+}  // namespace
 static void SaveValue(void* arg, const Slice& ikey, const Slice& v) {
   Saver* s = reinterpret_cast<Saver*>(arg);
   ParsedInternalKey parsed_key;
@@ -275,8 +279,7 @@ static bool NewestFirst(FileMetaData* a, FileMetaData* b) {
   return a->number > b->number;
 }
 
-void Version::ForEachOverlapping(Slice user_key, Slice internal_key,
-                                 void* arg,
+void Version::ForEachOverlapping(Slice user_key, Slice internal_key, void* arg,
                                  bool (*func)(void*, int, FileMetaData*)) {
   // TODO(sanjay): Change Version::Get() to use this function.
   const Comparator* ucmp = vset_->icmp_.user_comparator();
@@ -320,23 +323,21 @@ void Version::ForEachOverlapping(Slice user_key, Slice internal_key,
   }
 }
 
-Status Version::Get(const ReadOptions& options,
-                    const LookupKey& k,
-                    std::string* value,
-                    GetStats* stats) {
+Status Version::Get(const ReadOptions& options, const LookupKey& k,
+                    std::string* value, GetStats* stats) {
   Slice ikey = k.internal_key();
   Slice user_key = k.user_key();
   const Comparator* ucmp = vset_->icmp_.user_comparator();
   Status s;
 
-  stats->seek_file = NULL;
+  stats->seek_file = nullptr;
   stats->seek_file_level = -1;
-  FileMetaData* last_file_read = NULL;
+  FileMetaData* last_file_read = nullptr;
   int last_file_read_level = -1;
 
   // We can search level-by-level since entries never hop across
   // levels.  Therefore we are guaranteed that if we find data
-  // in an smaller level, later levels are irrelevant.
+  // in a smaller level, later levels are irrelevant.
   std::vector<FileMetaData*> tmp;
   FileMetaData* tmp2;
   for (int level = 0; level < config::kNumLevels; level++) {
@@ -365,13 +366,13 @@ Status Version::Get(const ReadOptions& options,
       // Binary search to find earliest index whose largest key >= ikey.
       uint32_t index = FindFile(vset_->icmp_, files_[level], ikey);
       if (index >= num_files) {
-        files = NULL;
+        files = nullptr;
         num_files = 0;
       } else {
         tmp2 = files[index];
         if (ucmp->Compare(user_key, tmp2->smallest.user_key()) < 0) {
           // All of "tmp2" is past any data for user_key
-          files = NULL;
+          files = nullptr;
           num_files = 0;
         } else {
           files = &tmp2;
@@ -381,7 +382,7 @@ Status Version::Get(const ReadOptions& options,
     }
 
     for (uint32_t i = 0; i < num_files; ++i) {
-      if (last_file_read != NULL && stats->seek_file == NULL) {
+      if (last_file_read != nullptr && stats->seek_file == nullptr) {
         // We have had more than one seek for this read.  Charge the 1st file.
         stats->seek_file = last_file_read;
         stats->seek_file_level = last_file_read_level;
@@ -396,14 +397,14 @@ Status Version::Get(const ReadOptions& options,
       saver.ucmp = ucmp;
       saver.user_key = user_key;
       saver.value = value;
-      s = vset_->table_cache_->Get(options, f->number, f->file_size,
-                                   ikey, &saver, SaveValue);
+      s = vset_->table_cache_->Get(options, f->number, f->file_size, ikey,
+                                   &saver, SaveValue);
       if (!s.ok()) {
         return s;
       }
       switch (saver.state) {
         case kNotFound:
-          break;      // Keep searching in other files
+          break;  // Keep searching in other files
         case kFound:
           return s;
         case kDeleted:
@@ -421,9 +422,9 @@ Status Version::Get(const ReadOptions& options,
 
 bool Version::UpdateStats(const GetStats& stats) {
   FileMetaData* f = stats.seek_file;
-  if (f != NULL) {
+  if (f != nullptr) {
     f->allowed_seeks--;
-    if (f->allowed_seeks <= 0 && file_to_compact_ == NULL) {
+    if (f->allowed_seeks <= 0 && file_to_compact_ == nullptr) {
       file_to_compact_ = f;
       file_to_compact_level_ = stats.seek_file_level;
       return true;
@@ -470,9 +471,7 @@ bool Version::RecordReadSample(Slice internal_key) {
   return false;
 }
 
-void Version::Ref() {
-  ++refs_;
-}
+void Version::Ref() { ++refs_; }
 
 void Version::Unref() {
   assert(this != &vset_->dummy_versions_);
@@ -483,16 +482,14 @@ void Version::Unref() {
   }
 }
 
-bool Version::OverlapInLevel(int level,
-                             const Slice* smallest_user_key,
+bool Version::OverlapInLevel(int level, const Slice* smallest_user_key,
                              const Slice* largest_user_key) {
   return SomeFileOverlapsRange(vset_->icmp_, (level > 0), files_[level],
                                smallest_user_key, largest_user_key);
 }
 
-int Version::PickLevelForMemTableOutput(
-    const Slice& smallest_user_key,
-    const Slice& largest_user_key) {
+int Version::PickLevelForMemTableOutput(const Slice& smallest_user_key,
+                                        const Slice& largest_user_key) {
   int level = 0;
   if (!OverlapInLevel(0, &smallest_user_key, &largest_user_key)) {
     // Push to next level if there is no overlap in next level,
@@ -508,7 +505,7 @@ int Version::PickLevelForMemTableOutput(
         // Check that file does not overlap too many grandparent bytes.
         GetOverlappingInputs(level + 2, &start, &limit, &overlaps);
         const int64_t sum = TotalFileSize(overlaps);
-        if (sum > kMaxGrandParentOverlapBytes) {
+        if (sum > MaxGrandParentOverlapBytes(vset_->options_)) {
           break;
         }
       }
@@ -519,40 +516,39 @@ int Version::PickLevelForMemTableOutput(
 }
 
 // Store in "*inputs" all files in "level" that overlap [begin,end]
-void Version::GetOverlappingInputs(
-    int level,
-    const InternalKey* begin,
-    const InternalKey* end,
-    std::vector<FileMetaData*>* inputs) {
+void Version::GetOverlappingInputs(int level, const InternalKey* begin,
+                                   const InternalKey* end,
+                                   std::vector<FileMetaData*>* inputs) {
   assert(level >= 0);
   assert(level < config::kNumLevels);
   inputs->clear();
   Slice user_begin, user_end;
-  if (begin != NULL) {
+  if (begin != nullptr) {
     user_begin = begin->user_key();
   }
-  if (end != NULL) {
+  if (end != nullptr) {
     user_end = end->user_key();
   }
   const Comparator* user_cmp = vset_->icmp_.user_comparator();
-  for (size_t i = 0; i < files_[level].size(); ) {
+  for (size_t i = 0; i < files_[level].size();) {
     FileMetaData* f = files_[level][i++];
     const Slice file_start = f->smallest.user_key();
     const Slice file_limit = f->largest.user_key();
-    if (begin != NULL && user_cmp->Compare(file_limit, user_begin) < 0) {
+    if (begin != nullptr && user_cmp->Compare(file_limit, user_begin) < 0) {
       // "f" is completely before specified range; skip it
-    } else if (end != NULL && user_cmp->Compare(file_start, user_end) > 0) {
+    } else if (end != nullptr && user_cmp->Compare(file_start, user_end) > 0) {
       // "f" is completely after specified range; skip it
     } else {
       inputs->push_back(f);
       if (level == 0) {
         // Level-0 files may overlap each other.  So check if the newly
         // added file has expanded the range.  If so, restart search.
-        if (begin != NULL && user_cmp->Compare(file_start, user_begin) < 0) {
+        if (begin != nullptr && user_cmp->Compare(file_start, user_begin) < 0) {
           user_begin = file_start;
           inputs->clear();
           i = 0;
-        } else if (end != NULL && user_cmp->Compare(file_limit, user_end) > 0) {
+        } else if (end != nullptr &&
+                   user_cmp->Compare(file_limit, user_end) > 0) {
           user_end = file_limit;
           inputs->clear();
           i = 0;
@@ -620,9 +616,7 @@ class VersionSet::Builder {
 
  public:
   // Initialize a builder with the files from *base and other info from *vset
-  Builder(VersionSet* vset, Version* base)
-      : vset_(vset),
-        base_(base) {
+  Builder(VersionSet* vset, Version* base) : vset_(vset), base_(base) {
     base_->Ref();
     BySmallestKey cmp;
     cmp.internal_comparator = &vset_->icmp_;
@@ -636,8 +630,8 @@ class VersionSet::Builder {
       const FileSet* added = levels_[level].added_files;
       std::vector<FileMetaData*> to_unref;
       to_unref.reserve(added->size());
-      for (FileSet::const_iterator it = added->begin();
-          it != added->end(); ++it) {
+      for (FileSet::const_iterator it = added->begin(); it != added->end();
+           ++it) {
         to_unref.push_back(*it);
       }
       delete added;
@@ -662,12 +656,9 @@ class VersionSet::Builder {
     }
 
     // Delete files
-    const VersionEdit::DeletedFileSet& del = edit->deleted_files_;
-    for (VersionEdit::DeletedFileSet::const_iterator iter = del.begin();
-         iter != del.end();
-         ++iter) {
-      const int level = iter->first;
-      const uint64_t number = iter->second;
+    for (const auto& deleted_file_set_kvp : edit->deleted_files_) {
+      const int level = deleted_file_set_kvp.first;
+      const uint64_t number = deleted_file_set_kvp.second;
       levels_[level].deleted_files.insert(number);
     }
 
@@ -690,7 +681,7 @@ class VersionSet::Builder {
       // same as the compaction of 40KB of data.  We are a little
       // conservative and allow approximately one seek for every 16KB
       // of data before triggering a compaction.
-      f->allowed_seeks = (f->file_size / 16384);
+      f->allowed_seeks = static_cast<int>((f->file_size / 16384U));
       if (f->allowed_seeks < 100) f->allowed_seeks = 100;
 
       levels_[level].deleted_files.erase(f->number);
@@ -708,20 +699,17 @@ class VersionSet::Builder {
       const std::vector<FileMetaData*>& base_files = base_->files_[level];
       std::vector<FileMetaData*>::const_iterator base_iter = base_files.begin();
       std::vector<FileMetaData*>::const_iterator base_end = base_files.end();
-      const FileSet* added = levels_[level].added_files;
-      v->files_[level].reserve(base_files.size() + added->size());
-      for (FileSet::const_iterator added_iter = added->begin();
-           added_iter != added->end();
-           ++added_iter) {
+      const FileSet* added_files = levels_[level].added_files;
+      v->files_[level].reserve(base_files.size() + added_files->size());
+      for (const auto& added_file : *added_files) {
         // Add all smaller files listed in base_
-        for (std::vector<FileMetaData*>::const_iterator bpos
-                 = std::upper_bound(base_iter, base_end, *added_iter, cmp);
-             base_iter != bpos;
-             ++base_iter) {
+        for (std::vector<FileMetaData*>::const_iterator bpos =
+                 std::upper_bound(base_iter, base_end, added_file, cmp);
+             base_iter != bpos; ++base_iter) {
           MaybeAddFile(v, level, *base_iter);
         }
 
-        MaybeAddFile(v, level, *added_iter);
+        MaybeAddFile(v, level, added_file);
       }
 
       // Add remaining base files
@@ -733,7 +721,7 @@ class VersionSet::Builder {
       // Make sure there is no overlap in levels > 0
       if (level > 0) {
         for (uint32_t i = 1; i < v->files_[level].size(); i++) {
-          const InternalKey& prev_end = v->files_[level][i-1]->largest;
+          const InternalKey& prev_end = v->files_[level][i - 1]->largest;
           const InternalKey& this_begin = v->files_[level][i]->smallest;
           if (vset_->icmp_.Compare(prev_end, this_begin) >= 0) {
             fprintf(stderr, "overlapping ranges in same level %s vs. %s\n",
@@ -754,7 +742,7 @@ class VersionSet::Builder {
       std::vector<FileMetaData*>* files = &v->files_[level];
       if (level > 0 && !files->empty()) {
         // Must not overlap
-        assert(vset_->icmp_.Compare((*files)[files->size()-1]->largest,
+        assert(vset_->icmp_.Compare((*files)[files->size() - 1]->largest,
                                     f->smallest) < 0);
       }
       f->refs++;
@@ -763,8 +751,7 @@ class VersionSet::Builder {
   }
 };
 
-VersionSet::VersionSet(const std::string& dbname,
-                       const Options* options,
+VersionSet::VersionSet(const std::string& dbname, const Options* options,
                        TableCache* table_cache,
                        const InternalKeyComparator* cmp)
     : env_(options->env),
@@ -777,10 +764,10 @@ VersionSet::VersionSet(const std::string& dbname,
       last_sequence_(0),
       log_number_(0),
       prev_log_number_(0),
-      descriptor_file_(NULL),
-      descriptor_log_(NULL),
+      descriptor_file_(nullptr),
+      descriptor_log_(nullptr),
       dummy_versions_(this),
-      current_(NULL) {
+      current_(nullptr) {
   AppendVersion(new Version(this));
 }
 
@@ -795,7 +782,7 @@ void VersionSet::AppendVersion(Version* v) {
   // Make "v" current
   assert(v->refs_ == 0);
   assert(v != current_);
-  if (current_ != NULL) {
+  if (current_ != nullptr) {
     current_->Unref();
   }
   current_ = v;
@@ -835,10 +822,10 @@ Status VersionSet::LogAndApply(VersionEdit* edit, port::Mutex* mu) {
   // a temporary file that contains a snapshot of the current version.
   std::string new_manifest_file;
   Status s;
-  if (descriptor_log_ == NULL) {
+  if (descriptor_log_ == nullptr) {
     // No reason to unlock *mu here since we only hit this path in the
     // first call to LogAndApply (when opening the database).
-    assert(descriptor_file_ == NULL);
+    assert(descriptor_file_ == nullptr);
     new_manifest_file = DescriptorFileName(dbname_, manifest_file_number_);
     edit->SetNextFile(next_file_number_);
     s = env_->NewWritableFile(new_manifest_file, &descriptor_file_);
@@ -884,8 +871,8 @@ Status VersionSet::LogAndApply(VersionEdit* edit, port::Mutex* mu) {
     if (!new_manifest_file.empty()) {
       delete descriptor_log_;
       delete descriptor_file_;
-      descriptor_log_ = NULL;
-      descriptor_file_ = NULL;
+      descriptor_log_ = nullptr;
+      descriptor_file_ = nullptr;
       env_->DeleteFile(new_manifest_file);
     }
   }
@@ -893,10 +880,10 @@ Status VersionSet::LogAndApply(VersionEdit* edit, port::Mutex* mu) {
   return s;
 }
 
-Status VersionSet::Recover() {
+Status VersionSet::Recover(bool* save_manifest) {
   struct LogReporter : public log::Reader::Reporter {
     Status* status;
-    virtual void Corruption(size_t bytes, const Status& s) {
+    void Corruption(size_t bytes, const Status& s) override {
       if (this->status->ok()) *this->status = s;
     }
   };
@@ -907,7 +894,7 @@ Status VersionSet::Recover() {
   if (!s.ok()) {
     return s;
   }
-  if (current.empty() || current[current.size()-1] != '\n') {
+  if (current.empty() || current[current.size() - 1] != '\n') {
     return Status::Corruption("CURRENT file does not end with newline");
   }
   current.resize(current.size() - 1);
@@ -916,6 +903,10 @@ Status VersionSet::Recover() {
   SequentialFile* file;
   s = env_->NewSequentialFile(dscname, &file);
   if (!s.ok()) {
+    if (s.IsNotFound()) {
+      return Status::Corruption("CURRENT points to a non-existent file",
+                                s.ToString());
+    }
     return s;
   }
 
@@ -932,7 +923,8 @@ Status VersionSet::Recover() {
   {
     LogReporter reporter;
     reporter.status = &s;
-    log::Reader reader(file, &reporter, true/*checksum*/, 0/*initial_offset*/);
+    log::Reader reader(file, &reporter, true /*checksum*/,
+                       0 /*initial_offset*/);
     Slice record;
     std::string scratch;
     while (reader.ReadRecord(&record, &scratch) && s.ok()) {
@@ -973,7 +965,7 @@ Status VersionSet::Recover() {
     }
   }
   delete file;
-  file = NULL;
+  file = nullptr;
 
   if (s.ok()) {
     if (!have_next_file) {
@@ -1003,11 +995,49 @@ Status VersionSet::Recover() {
     last_sequence_ = last_sequence;
     log_number_ = log_number;
     prev_log_number_ = prev_log_number;
+
+    // See if we can reuse the existing MANIFEST file.
+    if (ReuseManifest(dscname, current)) {
+      // No need to save new manifest
+    } else {
+      *save_manifest = true;
+    }
   }
 
   return s;
 }
 
+bool VersionSet::ReuseManifest(const std::string& dscname,
+                               const std::string& dscbase) {
+  if (!options_->reuse_logs) {
+    return false;
+  }
+  FileType manifest_type;
+  uint64_t manifest_number;
+  uint64_t manifest_size;
+  if (!ParseFileName(dscbase, &manifest_number, &manifest_type) ||
+      manifest_type != kDescriptorFile ||
+      !env_->GetFileSize(dscname, &manifest_size).ok() ||
+      // Make new compacted MANIFEST if old one is too big
+      manifest_size >= TargetFileSize(options_)) {
+    return false;
+  }
+
+  assert(descriptor_file_ == nullptr);
+  assert(descriptor_log_ == nullptr);
+  Status r = env_->NewAppendableFile(dscname, &descriptor_file_);
+  if (!r.ok()) {
+    Log(options_->info_log, "Reuse MANIFEST: %s\n", r.ToString().c_str());
+    assert(descriptor_file_ == nullptr);
+    return false;
+  }
+
+  Log(options_->info_log, "Reusing MANIFEST %s\n", dscname.c_str());
+  descriptor_log_ = new log::Writer(descriptor_file_, manifest_size);
+  manifest_file_number_ = manifest_number;
+  return true;
+}
+
 void VersionSet::MarkFileNumberUsed(uint64_t number) {
   if (next_file_number_ <= number) {
     next_file_number_ = number + 1;
@@ -1019,7 +1049,7 @@ void VersionSet::Finalize(Version* v) {
   int best_level = -1;
   double best_score = -1;
 
-  for (int level = 0; level < config::kNumLevels-1; level++) {
+  for (int level = 0; level < config::kNumLevels - 1; level++) {
     double score;
     if (level == 0) {
       // We treat level-0 specially by bounding the number of files
@@ -1034,11 +1064,12 @@ void VersionSet::Finalize(Version* v) {
       // setting, or very high compression ratios, or lots of
       // overwrites/deletions).
       score = v->files_[level].size() /
-          static_cast<double>(config::kL0_CompactionTrigger);
+              static_cast<double>(config::kL0_CompactionTrigger);
     } else {
       // Compute the ratio of current size to size limit.
       const uint64_t level_bytes = TotalFileSize(v->files_[level]);
-      score = static_cast<double>(level_bytes) / MaxBytesForLevel(level);
+      score =
+          static_cast<double>(level_bytes) / MaxBytesForLevel(options_, level);
     }
 
     if (score > best_score) {
@@ -1089,16 +1120,12 @@ int VersionSet::NumLevelFiles(int level) const {
 
 const char* VersionSet::LevelSummary(LevelSummaryStorage* scratch) const {
   // Update code if kNumLevels changes
-  assert(config::kNumLevels == 7);
+  static_assert(config::kNumLevels == 7, "");
   snprintf(scratch->buffer, sizeof(scratch->buffer),
-           "files[ %d %d %d %d %d %d %d ]",
-           int(current_->files_[0].size()),
-           int(current_->files_[1].size()),
-           int(current_->files_[2].size()),
-           int(current_->files_[3].size()),
-           int(current_->files_[4].size()),
-           int(current_->files_[5].size()),
-           int(current_->files_[6].size()));
+           "files[ %d %d %d %d %d %d %d ]", int(current_->files_[0].size()),
+           int(current_->files_[1].size()), int(current_->files_[2].size()),
+           int(current_->files_[3].size()), int(current_->files_[4].size()),
+           int(current_->files_[5].size()), int(current_->files_[6].size()));
   return scratch->buffer;
 }
 
@@ -1124,7 +1151,7 @@ uint64_t VersionSet::ApproximateOffsetOf(Version* v, const InternalKey& ikey) {
         Table* tableptr;
         Iterator* iter = table_cache_->NewIterator(
             ReadOptions(), files[i]->number, files[i]->file_size, &tableptr);
-        if (tableptr != NULL) {
+        if (tableptr != nullptr) {
           result += tableptr->ApproximateOffsetOf(ikey.Encode());
         }
         delete iter;
@@ -1135,8 +1162,7 @@ uint64_t VersionSet::ApproximateOffsetOf(Version* v, const InternalKey& ikey) {
 }
 
 void VersionSet::AddLiveFiles(std::set<uint64_t>* live) {
-  for (Version* v = dummy_versions_.next_;
-       v != &dummy_versions_;
+  for (Version* v = dummy_versions_.next_; v != &dummy_versions_;
        v = v->next_) {
     for (int level = 0; level < config::kNumLevels; level++) {
       const std::vector<FileMetaData*>& files = v->files_[level];
@@ -1159,7 +1185,7 @@ int64_t VersionSet::MaxNextLevelOverlappingBytes() {
   for (int level = 1; level < config::kNumLevels - 1; level++) {
     for (size_t i = 0; i < current_->files_[level].size(); i++) {
       const FileMetaData* f = current_->files_[level][i];
-      current_->GetOverlappingInputs(level+1, &f->smallest, &f->largest,
+      current_->GetOverlappingInputs(level + 1, &f->smallest, &f->largest,
                                      &overlaps);
       const int64_t sum = TotalFileSize(overlaps);
       if (sum > result) {
@@ -1174,8 +1200,7 @@ int64_t VersionSet::MaxNextLevelOverlappingBytes() {
 // *smallest, *largest.
 // REQUIRES: inputs is not empty
 void VersionSet::GetRange(const std::vector<FileMetaData*>& inputs,
-                          InternalKey* smallest,
-                          InternalKey* largest) {
+                          InternalKey* smallest, InternalKey* largest) {
   assert(!inputs.empty());
   smallest->Clear();
   largest->Clear();
@@ -1200,8 +1225,7 @@ void VersionSet::GetRange(const std::vector<FileMetaData*>& inputs,
 // REQUIRES: inputs is not empty
 void VersionSet::GetRange2(const std::vector<FileMetaData*>& inputs1,
                            const std::vector<FileMetaData*>& inputs2,
-                           InternalKey* smallest,
-                           InternalKey* largest) {
+                           InternalKey* smallest, InternalKey* largest) {
   std::vector<FileMetaData*> all = inputs1;
   all.insert(all.end(), inputs2.begin(), inputs2.end());
   GetRange(all, smallest, largest);
@@ -1223,8 +1247,8 @@ Iterator* VersionSet::MakeInputIterator(Compaction* c) {
       if (c->level() + which == 0) {
         const std::vector<FileMetaData*>& files = c->inputs_[which];
         for (size_t i = 0; i < files.size(); i++) {
-          list[num++] = table_cache_->NewIterator(
-              options, files[i]->number, files[i]->file_size);
+          list[num++] = table_cache_->NewIterator(options, files[i]->number,
+                                                  files[i]->file_size);
         }
       } else {
         // Create concatenating iterator for the files from this level
@@ -1247,12 +1271,12 @@ Compaction* VersionSet::PickCompaction() {
   // We prefer compactions triggered by too much data in a level over
   // the compactions triggered by seeks.
   const bool size_compaction = (current_->compaction_score_ >= 1);
-  const bool seek_compaction = (current_->file_to_compact_ != NULL);
+  const bool seek_compaction = (current_->file_to_compact_ != nullptr);
   if (size_compaction) {
     level = current_->compaction_level_;
     assert(level >= 0);
-    assert(level+1 < config::kNumLevels);
-    c = new Compaction(level);
+    assert(level + 1 < config::kNumLevels);
+    c = new Compaction(options_, level);
 
     // Pick the first file that comes after compact_pointer_[level]
     for (size_t i = 0; i < current_->files_[level].size(); i++) {
@@ -1269,10 +1293,10 @@ Compaction* VersionSet::PickCompaction() {
     }
   } else if (seek_compaction) {
     level = current_->file_to_compact_level_;
-    c = new Compaction(level);
+    c = new Compaction(options_, level);
     c->inputs_[0].push_back(current_->file_to_compact_);
   } else {
-    return NULL;
+    return nullptr;
   }
 
   c->input_version_ = current_;
@@ -1294,12 +1318,94 @@ Compaction* VersionSet::PickCompaction() {
   return c;
 }
 
+// Finds the largest key in a vector of files. Returns true if files it not
+// empty.
+bool FindLargestKey(const InternalKeyComparator& icmp,
+                    const std::vector<FileMetaData*>& files,
+                    InternalKey* largest_key) {
+  if (files.empty()) {
+    return false;
+  }
+  *largest_key = files[0]->largest;
+  for (size_t i = 1; i < files.size(); ++i) {
+    FileMetaData* f = files[i];
+    if (icmp.Compare(f->largest, *largest_key) > 0) {
+      *largest_key = f->largest;
+    }
+  }
+  return true;
+}
+
+// Finds minimum file b2=(l2, u2) in level file for which l2 > u1 and
+// user_key(l2) = user_key(u1)
+FileMetaData* FindSmallestBoundaryFile(
+    const InternalKeyComparator& icmp,
+    const std::vector<FileMetaData*>& level_files,
+    const InternalKey& largest_key) {
+  const Comparator* user_cmp = icmp.user_comparator();
+  FileMetaData* smallest_boundary_file = nullptr;
+  for (size_t i = 0; i < level_files.size(); ++i) {
+    FileMetaData* f = level_files[i];
+    if (icmp.Compare(f->smallest, largest_key) > 0 &&
+        user_cmp->Compare(f->smallest.user_key(), largest_key.user_key()) ==
+            0) {
+      if (smallest_boundary_file == nullptr ||
+          icmp.Compare(f->smallest, smallest_boundary_file->smallest) < 0) {
+        smallest_boundary_file = f;
+      }
+    }
+  }
+  return smallest_boundary_file;
+}
+
+// Extracts the largest file b1 from |compaction_files| and then searches for a
+// b2 in |level_files| for which user_key(u1) = user_key(l2). If it finds such a
+// file b2 (known as a boundary file) it adds it to |compaction_files| and then
+// searches again using this new upper bound.
+//
+// If there are two blocks, b1=(l1, u1) and b2=(l2, u2) and
+// user_key(u1) = user_key(l2), and if we compact b1 but not b2 then a
+// subsequent get operation will yield an incorrect result because it will
+// return the record from b2 in level i rather than from b1 because it searches
+// level by level for records matching the supplied user key.
+//
+// parameters:
+//   in     level_files:      List of files to search for boundary files.
+//   in/out compaction_files: List of files to extend by adding boundary files.
+void AddBoundaryInputs(const InternalKeyComparator& icmp,
+                       const std::vector<FileMetaData*>& level_files,
+                       std::vector<FileMetaData*>* compaction_files) {
+  InternalKey largest_key;
+
+  // Quick return if compaction_files is empty.
+  if (!FindLargestKey(icmp, *compaction_files, &largest_key)) {
+    return;
+  }
+
+  bool continue_searching = true;
+  while (continue_searching) {
+    FileMetaData* smallest_boundary_file =
+        FindSmallestBoundaryFile(icmp, level_files, largest_key);
+
+    // If a boundary file was found advance largest_key, otherwise we're done.
+    if (smallest_boundary_file != NULL) {
+      compaction_files->push_back(smallest_boundary_file);
+      largest_key = smallest_boundary_file->largest;
+    } else {
+      continue_searching = false;
+    }
+  }
+}
+
 void VersionSet::SetupOtherInputs(Compaction* c) {
   const int level = c->level();
   InternalKey smallest, largest;
+
+  AddBoundaryInputs(icmp_, current_->files_[level], &c->inputs_[0]);
   GetRange(c->inputs_[0], &smallest, &largest);
 
-  current_->GetOverlappingInputs(level+1, &smallest, &largest, &c->inputs_[1]);
+  current_->GetOverlappingInputs(level + 1, &smallest, &largest,
+                                 &c->inputs_[1]);
 
   // Get entire range covered by compaction
   InternalKey all_start, all_limit;
@@ -1310,26 +1416,24 @@ void VersionSet::SetupOtherInputs(Compaction* c) {
   if (!c->inputs_[1].empty()) {
     std::vector<FileMetaData*> expanded0;
     current_->GetOverlappingInputs(level, &all_start, &all_limit, &expanded0);
+    AddBoundaryInputs(icmp_, current_->files_[level], &expanded0);
     const int64_t inputs0_size = TotalFileSize(c->inputs_[0]);
     const int64_t inputs1_size = TotalFileSize(c->inputs_[1]);
     const int64_t expanded0_size = TotalFileSize(expanded0);
     if (expanded0.size() > c->inputs_[0].size() &&
-        inputs1_size + expanded0_size < kExpandedCompactionByteSizeLimit) {
+        inputs1_size + expanded0_size <
+            ExpandedCompactionByteSizeLimit(options_)) {
       InternalKey new_start, new_limit;
       GetRange(expanded0, &new_start, &new_limit);
       std::vector<FileMetaData*> expanded1;
-      current_->GetOverlappingInputs(level+1, &new_start, &new_limit,
+      current_->GetOverlappingInputs(level + 1, &new_start, &new_limit,
                                      &expanded1);
       if (expanded1.size() == c->inputs_[1].size()) {
         Log(options_->info_log,
             "Expanding@%d %d+%d (%ld+%ld bytes) to %d+%d (%ld+%ld bytes)\n",
-            level,
-            int(c->inputs_[0].size()),
-            int(c->inputs_[1].size()),
-            long(inputs0_size), long(inputs1_size),
-            int(expanded0.size()),
-            int(expanded1.size()),
-            long(expanded0_size), long(inputs1_size));
+            level, int(c->inputs_[0].size()), int(c->inputs_[1].size()),
+            long(inputs0_size), long(inputs1_size), int(expanded0.size()),
+            int(expanded1.size()), long(expanded0_size), long(inputs1_size));
         smallest = new_start;
         largest = new_limit;
         c->inputs_[0] = expanded0;
@@ -1346,13 +1450,6 @@ void VersionSet::SetupOtherInputs(Compaction* c) {
                                    &c->grandparents_);
   }
 
-  if (false) {
-    Log(options_->info_log, "Compacting %d '%s' .. '%s'",
-        level,
-        smallest.DebugString().c_str(),
-        largest.DebugString().c_str());
-  }
-
   // Update the place where we will do the next compaction for this level.
   // We update this immediately instead of waiting for the VersionEdit
   // to be applied so that if the compaction fails, we will try a different
@@ -1361,14 +1458,12 @@ void VersionSet::SetupOtherInputs(Compaction* c) {
   c->edit_.SetCompactPointer(level, largest);
 }
 
-Compaction* VersionSet::CompactRange(
-    int level,
-    const InternalKey* begin,
-    const InternalKey* end) {
+Compaction* VersionSet::CompactRange(int level, const InternalKey* begin,
+                                     const InternalKey* end) {
   std::vector<FileMetaData*> inputs;
   current_->GetOverlappingInputs(level, begin, end, &inputs);
   if (inputs.empty()) {
-    return NULL;
+    return nullptr;
   }
 
   // Avoid compacting too much in one shot in case the range is large.
@@ -1376,7 +1471,7 @@ Compaction* VersionSet::CompactRange(
   // and we must not pick one file and drop another older file if the
   // two files overlap.
   if (level > 0) {
-    const uint64_t limit = MaxFileSizeForLevel(level);
+    const uint64_t limit = MaxFileSizeForLevel(options_, level);
     uint64_t total = 0;
     for (size_t i = 0; i < inputs.size(); i++) {
       uint64_t s = inputs[i]->file_size;
@@ -1388,7 +1483,7 @@ Compaction* VersionSet::CompactRange(
     }
   }
 
-  Compaction* c = new Compaction(level);
+  Compaction* c = new Compaction(options_, level);
   c->input_version_ = current_;
   c->input_version_->Ref();
   c->inputs_[0] = inputs;
@@ -1396,10 +1491,10 @@ Compaction* VersionSet::CompactRange(
   return c;
 }
 
-Compaction::Compaction(int level)
+Compaction::Compaction(const Options* options, int level)
     : level_(level),
-      max_output_file_size_(MaxFileSizeForLevel(level)),
-      input_version_(NULL),
+      max_output_file_size_(MaxFileSizeForLevel(options, level)),
+      input_version_(nullptr),
       grandparent_index_(0),
       seen_key_(false),
       overlapped_bytes_(0) {
@@ -1409,18 +1504,19 @@ Compaction::Compaction(int level)
 }
 
 Compaction::~Compaction() {
-  if (input_version_ != NULL) {
+  if (input_version_ != nullptr) {
     input_version_->Unref();
   }
 }
 
 bool Compaction::IsTrivialMove() const {
+  const VersionSet* vset = input_version_->vset_;
   // Avoid a move if there is lots of overlapping grandparent data.
   // Otherwise, the move could create a parent file that will require
   // a very expensive merge later on.
-  return (num_input_files(0) == 1 &&
-          num_input_files(1) == 0 &&
-          TotalFileSize(grandparents_) <= kMaxGrandParentOverlapBytes);
+  return (num_input_files(0) == 1 && num_input_files(1) == 0 &&
+          TotalFileSize(grandparents_) <=
+              MaxGrandParentOverlapBytes(vset->options_));
 }
 
 void Compaction::AddInputDeletions(VersionEdit* edit) {
@@ -1436,7 +1532,7 @@ bool Compaction::IsBaseLevelForKey(const Slice& user_key) {
   const Comparator* user_cmp = input_version_->vset_->icmp_.user_comparator();
   for (int lvl = level_ + 2; lvl < config::kNumLevels; lvl++) {
     const std::vector<FileMetaData*>& files = input_version_->files_[lvl];
-    for (; level_ptrs_[lvl] < files.size(); ) {
+    while (level_ptrs_[lvl] < files.size()) {
       FileMetaData* f = files[level_ptrs_[lvl]];
       if (user_cmp->Compare(user_key, f->largest.user_key()) <= 0) {
         // We've advanced far enough
@@ -1453,11 +1549,13 @@ bool Compaction::IsBaseLevelForKey(const Slice& user_key) {
 }
 
 bool Compaction::ShouldStopBefore(const Slice& internal_key) {
+  const VersionSet* vset = input_version_->vset_;
   // Scan to find earliest grandparent file that contains key.
-  const InternalKeyComparator* icmp = &input_version_->vset_->icmp_;
+  const InternalKeyComparator* icmp = &vset->icmp_;
   while (grandparent_index_ < grandparents_.size() &&
-      icmp->Compare(internal_key,
-                    grandparents_[grandparent_index_]->largest.Encode()) > 0) {
+         icmp->Compare(internal_key,
+                       grandparents_[grandparent_index_]->largest.Encode()) >
+             0) {
     if (seen_key_) {
       overlapped_bytes_ += grandparents_[grandparent_index_]->file_size;
     }
@@ -1465,7 +1563,7 @@ bool Compaction::ShouldStopBefore(const Slice& internal_key) {
   }
   seen_key_ = true;
 
-  if (overlapped_bytes_ > kMaxGrandParentOverlapBytes) {
+  if (overlapped_bytes_ > MaxGrandParentOverlapBytes(vset->options_)) {
     // Too much overlap for current output; start new output
     overlapped_bytes_ = 0;
     return true;
@@ -1475,9 +1573,9 @@ bool Compaction::ShouldStopBefore(const Slice& internal_key) {
 }
 
 void Compaction::ReleaseInputs() {
-  if (input_version_ != NULL) {
+  if (input_version_ != nullptr) {
     input_version_->Unref();
-    input_version_ = NULL;
+    input_version_ = nullptr;
   }
 }
 
diff --git a/db/version_set.h b/db/version_set.h
index 8dc14b8..69f3d70 100644
--- a/db/version_set.h
+++ b/db/version_set.h
@@ -18,6 +18,7 @@
 #include <map>
 #include <set>
 #include <vector>
+
 #include "db/dbformat.h"
 #include "db/version_edit.h"
 #include "port/port.h"
@@ -25,7 +26,9 @@
 
 namespace leveldb {
 
-namespace log { class Writer; }
+namespace log {
+class Writer;
+}
 
 class Compaction;
 class Iterator;
@@ -39,30 +42,23 @@ class WritableFile;
 // Return the smallest index i such that files[i]->largest >= key.
 // Return files.size() if there is no such file.
 // REQUIRES: "files" contains a sorted list of non-overlapping files.
-extern int FindFile(const InternalKeyComparator& icmp,
-                    const std::vector<FileMetaData*>& files,
-                    const Slice& key);
+int FindFile(const InternalKeyComparator& icmp,
+             const std::vector<FileMetaData*>& files, const Slice& key);
 
 // Returns true iff some file in "files" overlaps the user key range
 // [*smallest,*largest].
-// smallest==NULL represents a key smaller than all keys in the DB.
-// largest==NULL represents a key largest than all keys in the DB.
+// smallest==nullptr represents a key smaller than all keys in the DB.
+// largest==nullptr represents a key largest than all keys in the DB.
 // REQUIRES: If disjoint_sorted_files, files[] contains disjoint ranges
 //           in sorted order.
-extern bool SomeFileOverlapsRange(
-    const InternalKeyComparator& icmp,
-    bool disjoint_sorted_files,
-    const std::vector<FileMetaData*>& files,
-    const Slice* smallest_user_key,
-    const Slice* largest_user_key);
+bool SomeFileOverlapsRange(const InternalKeyComparator& icmp,
+                           bool disjoint_sorted_files,
+                           const std::vector<FileMetaData*>& files,
+                           const Slice* smallest_user_key,
+                           const Slice* largest_user_key);
 
 class Version {
  public:
-  // Append to *iters a sequence of iterators that will
-  // yield the contents of this Version when merged together.
-  // REQUIRES: This version has been saved (see VersionSet::SaveTo)
-  void AddIterators(const ReadOptions&, std::vector<Iterator*>* iters);
-
   // Lookup the value for key.  If found, store it in *val and
   // return OK.  Else return a non-OK status.  Fills *stats.
   // REQUIRES: lock is not held
@@ -70,6 +66,12 @@ class Version {
     FileMetaData* seek_file;
     int seek_file_level;
   };
+
+  // Append to *iters a sequence of iterators that will
+  // yield the contents of this Version when merged together.
+  // REQUIRES: This version has been saved (see VersionSet::SaveTo)
+  void AddIterators(const ReadOptions&, std::vector<Iterator*>* iters);
+
   Status Get(const ReadOptions&, const LookupKey& key, std::string* val,
              GetStats* stats);
 
@@ -91,16 +93,15 @@ class Version {
 
   void GetOverlappingInputs(
       int level,
-      const InternalKey* begin,         // NULL means before all keys
-      const InternalKey* end,           // NULL means after all keys
+      const InternalKey* begin,  // nullptr means before all keys
+      const InternalKey* end,    // nullptr means after all keys
       std::vector<FileMetaData*>* inputs);
 
   // Returns true iff some file in the specified level overlaps
   // some part of [*smallest_user_key,*largest_user_key].
-  // smallest_user_key==NULL represents a key smaller than all keys in the DB.
-  // largest_user_key==NULL represents a key largest than all keys in the DB.
-  bool OverlapInLevel(int level,
-                      const Slice* smallest_user_key,
+  // smallest_user_key==nullptr represents a key smaller than all the DB's keys.
+  // largest_user_key==nullptr represents a key largest than all the DB's keys.
+  bool OverlapInLevel(int level, const Slice* smallest_user_key,
                       const Slice* largest_user_key);
 
   // Return the level at which we should place a new memtable compaction
@@ -118,6 +119,22 @@ class Version {
   friend class VersionSet;
 
   class LevelFileNumIterator;
+
+  explicit Version(VersionSet* vset)
+      : vset_(vset),
+        next_(this),
+        prev_(this),
+        refs_(0),
+        file_to_compact_(nullptr),
+        file_to_compact_level_(-1),
+        compaction_score_(-1),
+        compaction_level_(-1) {}
+
+  Version(const Version&) = delete;
+  Version& operator=(const Version&) = delete;
+
+  ~Version();
+
   Iterator* NewConcatenatingIterator(const ReadOptions&, int level) const;
 
   // Call func(arg, level, f) for every file that overlaps user_key in
@@ -125,14 +142,13 @@ class Version {
   // false, makes no more calls.
   //
   // REQUIRES: user portion of internal_key == user_key.
-  void ForEachOverlapping(Slice user_key, Slice internal_key,
-                          void* arg,
+  void ForEachOverlapping(Slice user_key, Slice internal_key, void* arg,
                           bool (*func)(void*, int, FileMetaData*));
 
-  VersionSet* vset_;            // VersionSet to which this Version belongs
-  Version* next_;               // Next version in linked list
-  Version* prev_;               // Previous version in linked list
-  int refs_;                    // Number of live refs to this version
+  VersionSet* vset_;  // VersionSet to which this Version belongs
+  Version* next_;     // Next version in linked list
+  Version* prev_;     // Previous version in linked list
+  int refs_;          // Number of live refs to this version
 
   // List of files per level
   std::vector<FileMetaData*> files_[config::kNumLevels];
@@ -146,28 +162,15 @@ class Version {
   // are initialized by Finalize().
   double compaction_score_;
   int compaction_level_;
-
-  explicit Version(VersionSet* vset)
-      : vset_(vset), next_(this), prev_(this), refs_(0),
-        file_to_compact_(NULL),
-        file_to_compact_level_(-1),
-        compaction_score_(-1),
-        compaction_level_(-1) {
-  }
-
-  ~Version();
-
-  // No copying allowed
-  Version(const Version&);
-  void operator=(const Version&);
 };
 
 class VersionSet {
  public:
-  VersionSet(const std::string& dbname,
-             const Options* options,
-             TableCache* table_cache,
-             const InternalKeyComparator*);
+  VersionSet(const std::string& dbname, const Options* options,
+             TableCache* table_cache, const InternalKeyComparator*);
+  VersionSet(const VersionSet&) = delete;
+  VersionSet& operator=(const VersionSet&) = delete;
+
   ~VersionSet();
 
   // Apply *edit to the current version to form a new descriptor that
@@ -179,7 +182,7 @@ class VersionSet {
       EXCLUSIVE_LOCKS_REQUIRED(mu);
 
   // Recover the last saved descriptor from persistent storage.
-  Status Recover();
+  Status Recover(bool* save_manifest);
 
   // Return the current version.
   Version* current() const { return current_; }
@@ -225,19 +228,17 @@ class VersionSet {
   uint64_t PrevLogNumber() const { return prev_log_number_; }
 
   // Pick level and inputs for a new compaction.
-  // Returns NULL if there is no compaction to be done.
+  // Returns nullptr if there is no compaction to be done.
   // Otherwise returns a pointer to a heap-allocated object that
   // describes the compaction.  Caller should delete the result.
   Compaction* PickCompaction();
 
   // Return a compaction object for compacting the range [begin,end] in
-  // the specified level.  Returns NULL if there is nothing in that
+  // the specified level.  Returns nullptr if there is nothing in that
   // level that overlaps the specified range.  Caller should delete
   // the result.
-  Compaction* CompactRange(
-      int level,
-      const InternalKey* begin,
-      const InternalKey* end);
+  Compaction* CompactRange(int level, const InternalKey* begin,
+                           const InternalKey* end);
 
   // Return the maximum overlapping data (in bytes) at next level for any
   // file at a level >= 1.
@@ -250,7 +251,7 @@ class VersionSet {
   // Returns true iff some level needs a compaction.
   bool NeedsCompaction() const {
     Version* v = current_;
-    return (v->compaction_score_ >= 1) || (v->file_to_compact_ != NULL);
+    return (v->compaction_score_ >= 1) || (v->file_to_compact_ != nullptr);
   }
 
   // Add all files listed in any live version to *live.
@@ -274,16 +275,16 @@ class VersionSet {
   friend class Compaction;
   friend class Version;
 
+  bool ReuseManifest(const std::string& dscname, const std::string& dscbase);
+
   void Finalize(Version* v);
 
-  void GetRange(const std::vector<FileMetaData*>& inputs,
-                InternalKey* smallest,
+  void GetRange(const std::vector<FileMetaData*>& inputs, InternalKey* smallest,
                 InternalKey* largest);
 
   void GetRange2(const std::vector<FileMetaData*>& inputs1,
                  const std::vector<FileMetaData*>& inputs2,
-                 InternalKey* smallest,
-                 InternalKey* largest);
+                 InternalKey* smallest, InternalKey* largest);
 
   void SetupOtherInputs(Compaction* c);
 
@@ -312,10 +313,6 @@ class VersionSet {
   // Per-level key at which the next compaction at that level should start.
   // Either an empty string, or a valid InternalKey.
   std::string compact_pointer_[config::kNumLevels];
-
-  // No copying allowed
-  VersionSet(const VersionSet&);
-  void operator=(const VersionSet&);
 };
 
 // A Compaction encapsulates information about a compaction.
@@ -364,7 +361,7 @@ class Compaction {
   friend class Version;
   friend class VersionSet;
 
-  explicit Compaction(int level);
+  Compaction(const Options* options, int level);
 
   int level_;
   uint64_t max_output_file_size_;
@@ -372,9 +369,9 @@ class Compaction {
   VersionEdit edit_;
 
   // Each compaction reads inputs from "level_" and "level_+1"
-  std::vector<FileMetaData*> inputs_[2];      // The two sets of inputs
+  std::vector<FileMetaData*> inputs_[2];  // The two sets of inputs
 
-  // State used to check for number of of overlapping grandparent files
+  // State used to check for number of overlapping grandparent files
   // (parent == level_ + 1, grandparent == level_ + 2)
   std::vector<FileMetaData*> grandparents_;
   size_t grandparent_index_;  // Index in grandparent_starts_
diff --git a/db/version_set_test.cc b/db/version_set_test.cc
index 501e34d..c1056a1 100644
--- a/db/version_set_test.cc
+++ b/db/version_set_test.cc
@@ -11,10 +11,7 @@ namespace leveldb {
 
 class FindFileTest {
  public:
-  std::vector<FileMetaData*> files_;
-  bool disjoint_sorted_files_;
-
-  FindFileTest() : disjoint_sorted_files_(true) { }
+  FindFileTest() : disjoint_sorted_files_(true) {}
 
   ~FindFileTest() {
     for (int i = 0; i < files_.size(); i++) {
@@ -40,20 +37,25 @@ class FindFileTest {
 
   bool Overlaps(const char* smallest, const char* largest) {
     InternalKeyComparator cmp(BytewiseComparator());
-    Slice s(smallest != NULL ? smallest : "");
-    Slice l(largest != NULL ? largest : "");
+    Slice s(smallest != nullptr ? smallest : "");
+    Slice l(largest != nullptr ? largest : "");
     return SomeFileOverlapsRange(cmp, disjoint_sorted_files_, files_,
-                                 (smallest != NULL ? &s : NULL),
-                                 (largest != NULL ? &l : NULL));
+                                 (smallest != nullptr ? &s : nullptr),
+                                 (largest != nullptr ? &l : nullptr));
   }
+
+  bool disjoint_sorted_files_;
+
+ private:
+  std::vector<FileMetaData*> files_;
 };
 
 TEST(FindFileTest, Empty) {
   ASSERT_EQ(0, Find("foo"));
-  ASSERT_TRUE(! Overlaps("a", "z"));
-  ASSERT_TRUE(! Overlaps(NULL, "z"));
-  ASSERT_TRUE(! Overlaps("a", NULL));
-  ASSERT_TRUE(! Overlaps(NULL, NULL));
+  ASSERT_TRUE(!Overlaps("a", "z"));
+  ASSERT_TRUE(!Overlaps(nullptr, "z"));
+  ASSERT_TRUE(!Overlaps("a", nullptr));
+  ASSERT_TRUE(!Overlaps(nullptr, nullptr));
 }
 
 TEST(FindFileTest, Single) {
@@ -65,8 +67,8 @@ TEST(FindFileTest, Single) {
   ASSERT_EQ(1, Find("q1"));
   ASSERT_EQ(1, Find("z"));
 
-  ASSERT_TRUE(! Overlaps("a", "b"));
-  ASSERT_TRUE(! Overlaps("z1", "z2"));
+  ASSERT_TRUE(!Overlaps("a", "b"));
+  ASSERT_TRUE(!Overlaps("z1", "z2"));
   ASSERT_TRUE(Overlaps("a", "p"));
   ASSERT_TRUE(Overlaps("a", "q"));
   ASSERT_TRUE(Overlaps("a", "z"));
@@ -78,15 +80,14 @@ TEST(FindFileTest, Single) {
   ASSERT_TRUE(Overlaps("q", "q"));
   ASSERT_TRUE(Overlaps("q", "q1"));
 
-  ASSERT_TRUE(! Overlaps(NULL, "j"));
-  ASSERT_TRUE(! Overlaps("r", NULL));
-  ASSERT_TRUE(Overlaps(NULL, "p"));
-  ASSERT_TRUE(Overlaps(NULL, "p1"));
-  ASSERT_TRUE(Overlaps("q", NULL));
-  ASSERT_TRUE(Overlaps(NULL, NULL));
+  ASSERT_TRUE(!Overlaps(nullptr, "j"));
+  ASSERT_TRUE(!Overlaps("r", nullptr));
+  ASSERT_TRUE(Overlaps(nullptr, "p"));
+  ASSERT_TRUE(Overlaps(nullptr, "p1"));
+  ASSERT_TRUE(Overlaps("q", nullptr));
+  ASSERT_TRUE(Overlaps(nullptr, nullptr));
 }
 
-
 TEST(FindFileTest, Multiple) {
   Add("150", "200");
   Add("200", "250");
@@ -110,10 +111,10 @@ TEST(FindFileTest, Multiple) {
   ASSERT_EQ(3, Find("450"));
   ASSERT_EQ(4, Find("451"));
 
-  ASSERT_TRUE(! Overlaps("100", "149"));
-  ASSERT_TRUE(! Overlaps("251", "299"));
-  ASSERT_TRUE(! Overlaps("451", "500"));
-  ASSERT_TRUE(! Overlaps("351", "399"));
+  ASSERT_TRUE(!Overlaps("100", "149"));
+  ASSERT_TRUE(!Overlaps("251", "299"));
+  ASSERT_TRUE(!Overlaps("451", "500"));
+  ASSERT_TRUE(!Overlaps("351", "399"));
 
   ASSERT_TRUE(Overlaps("100", "150"));
   ASSERT_TRUE(Overlaps("100", "200"));
@@ -130,25 +131,25 @@ TEST(FindFileTest, MultipleNullBoundaries) {
   Add("200", "250");
   Add("300", "350");
   Add("400", "450");
-  ASSERT_TRUE(! Overlaps(NULL, "149"));
-  ASSERT_TRUE(! Overlaps("451", NULL));
-  ASSERT_TRUE(Overlaps(NULL, NULL));
-  ASSERT_TRUE(Overlaps(NULL, "150"));
-  ASSERT_TRUE(Overlaps(NULL, "199"));
-  ASSERT_TRUE(Overlaps(NULL, "200"));
-  ASSERT_TRUE(Overlaps(NULL, "201"));
-  ASSERT_TRUE(Overlaps(NULL, "400"));
-  ASSERT_TRUE(Overlaps(NULL, "800"));
-  ASSERT_TRUE(Overlaps("100", NULL));
-  ASSERT_TRUE(Overlaps("200", NULL));
-  ASSERT_TRUE(Overlaps("449", NULL));
-  ASSERT_TRUE(Overlaps("450", NULL));
+  ASSERT_TRUE(!Overlaps(nullptr, "149"));
+  ASSERT_TRUE(!Overlaps("451", nullptr));
+  ASSERT_TRUE(Overlaps(nullptr, nullptr));
+  ASSERT_TRUE(Overlaps(nullptr, "150"));
+  ASSERT_TRUE(Overlaps(nullptr, "199"));
+  ASSERT_TRUE(Overlaps(nullptr, "200"));
+  ASSERT_TRUE(Overlaps(nullptr, "201"));
+  ASSERT_TRUE(Overlaps(nullptr, "400"));
+  ASSERT_TRUE(Overlaps(nullptr, "800"));
+  ASSERT_TRUE(Overlaps("100", nullptr));
+  ASSERT_TRUE(Overlaps("200", nullptr));
+  ASSERT_TRUE(Overlaps("449", nullptr));
+  ASSERT_TRUE(Overlaps("450", nullptr));
 }
 
 TEST(FindFileTest, OverlapSequenceChecks) {
   Add("200", "200", 5000, 3000);
-  ASSERT_TRUE(! Overlaps("199", "199"));
-  ASSERT_TRUE(! Overlaps("201", "300"));
+  ASSERT_TRUE(!Overlaps("199", "199"));
+  ASSERT_TRUE(!Overlaps("201", "300"));
   ASSERT_TRUE(Overlaps("200", "200"));
   ASSERT_TRUE(Overlaps("190", "200"));
   ASSERT_TRUE(Overlaps("200", "210"));
@@ -158,8 +159,8 @@ TEST(FindFileTest, OverlappingFiles) {
   Add("150", "600");
   Add("400", "500");
   disjoint_sorted_files_ = false;
-  ASSERT_TRUE(! Overlaps("100", "149"));
-  ASSERT_TRUE(! Overlaps("601", "700"));
+  ASSERT_TRUE(!Overlaps("100", "149"));
+  ASSERT_TRUE(!Overlaps("601", "700"));
   ASSERT_TRUE(Overlaps("100", "150"));
   ASSERT_TRUE(Overlaps("100", "200"));
   ASSERT_TRUE(Overlaps("100", "300"));
@@ -172,8 +173,160 @@ TEST(FindFileTest, OverlappingFiles) {
   ASSERT_TRUE(Overlaps("600", "700"));
 }
 
-}  // namespace leveldb
+void AddBoundaryInputs(const InternalKeyComparator& icmp,
+                       const std::vector<FileMetaData*>& level_files,
+                       std::vector<FileMetaData*>* compaction_files);
+
+class AddBoundaryInputsTest {
+ public:
+  std::vector<FileMetaData*> level_files_;
+  std::vector<FileMetaData*> compaction_files_;
+  std::vector<FileMetaData*> all_files_;
+  InternalKeyComparator icmp_;
+
+  AddBoundaryInputsTest() : icmp_(BytewiseComparator()) {}
+
+  ~AddBoundaryInputsTest() {
+    for (size_t i = 0; i < all_files_.size(); ++i) {
+      delete all_files_[i];
+    }
+    all_files_.clear();
+  }
+
+  FileMetaData* CreateFileMetaData(uint64_t number, InternalKey smallest,
+                                   InternalKey largest) {
+    FileMetaData* f = new FileMetaData();
+    f->number = number;
+    f->smallest = smallest;
+    f->largest = largest;
+    all_files_.push_back(f);
+    return f;
+  }
+};
+
+TEST(AddBoundaryInputsTest, TestEmptyFileSets) {
+  AddBoundaryInputs(icmp_, level_files_, &compaction_files_);
+  ASSERT_TRUE(compaction_files_.empty());
+  ASSERT_TRUE(level_files_.empty());
+}
+
+TEST(AddBoundaryInputsTest, TestEmptyLevelFiles) {
+  FileMetaData* f1 =
+      CreateFileMetaData(1, InternalKey("100", 2, kTypeValue),
+                         InternalKey(InternalKey("100", 1, kTypeValue)));
+  compaction_files_.push_back(f1);
+
+  AddBoundaryInputs(icmp_, level_files_, &compaction_files_);
+  ASSERT_EQ(1, compaction_files_.size());
+  ASSERT_EQ(f1, compaction_files_[0]);
+  ASSERT_TRUE(level_files_.empty());
+}
+
+TEST(AddBoundaryInputsTest, TestEmptyCompactionFiles) {
+  FileMetaData* f1 =
+      CreateFileMetaData(1, InternalKey("100", 2, kTypeValue),
+                         InternalKey(InternalKey("100", 1, kTypeValue)));
+  level_files_.push_back(f1);
+
+  AddBoundaryInputs(icmp_, level_files_, &compaction_files_);
+  ASSERT_TRUE(compaction_files_.empty());
+  ASSERT_EQ(1, level_files_.size());
+  ASSERT_EQ(f1, level_files_[0]);
+}
+
+TEST(AddBoundaryInputsTest, TestNoBoundaryFiles) {
+  FileMetaData* f1 =
+      CreateFileMetaData(1, InternalKey("100", 2, kTypeValue),
+                         InternalKey(InternalKey("100", 1, kTypeValue)));
+  FileMetaData* f2 =
+      CreateFileMetaData(1, InternalKey("200", 2, kTypeValue),
+                         InternalKey(InternalKey("200", 1, kTypeValue)));
+  FileMetaData* f3 =
+      CreateFileMetaData(1, InternalKey("300", 2, kTypeValue),
+                         InternalKey(InternalKey("300", 1, kTypeValue)));
+
+  level_files_.push_back(f3);
+  level_files_.push_back(f2);
+  level_files_.push_back(f1);
+  compaction_files_.push_back(f2);
+  compaction_files_.push_back(f3);
+
+  AddBoundaryInputs(icmp_, level_files_, &compaction_files_);
+  ASSERT_EQ(2, compaction_files_.size());
+}
+
+TEST(AddBoundaryInputsTest, TestOneBoundaryFiles) {
+  FileMetaData* f1 =
+      CreateFileMetaData(1, InternalKey("100", 3, kTypeValue),
+                         InternalKey(InternalKey("100", 2, kTypeValue)));
+  FileMetaData* f2 =
+      CreateFileMetaData(1, InternalKey("100", 1, kTypeValue),
+                         InternalKey(InternalKey("200", 3, kTypeValue)));
+  FileMetaData* f3 =
+      CreateFileMetaData(1, InternalKey("300", 2, kTypeValue),
+                         InternalKey(InternalKey("300", 1, kTypeValue)));
+
+  level_files_.push_back(f3);
+  level_files_.push_back(f2);
+  level_files_.push_back(f1);
+  compaction_files_.push_back(f1);
+
+  AddBoundaryInputs(icmp_, level_files_, &compaction_files_);
+  ASSERT_EQ(2, compaction_files_.size());
+  ASSERT_EQ(f1, compaction_files_[0]);
+  ASSERT_EQ(f2, compaction_files_[1]);
+}
+
+TEST(AddBoundaryInputsTest, TestTwoBoundaryFiles) {
+  FileMetaData* f1 =
+      CreateFileMetaData(1, InternalKey("100", 6, kTypeValue),
+                         InternalKey(InternalKey("100", 5, kTypeValue)));
+  FileMetaData* f2 =
+      CreateFileMetaData(1, InternalKey("100", 2, kTypeValue),
+                         InternalKey(InternalKey("300", 1, kTypeValue)));
+  FileMetaData* f3 =
+      CreateFileMetaData(1, InternalKey("100", 4, kTypeValue),
+                         InternalKey(InternalKey("100", 3, kTypeValue)));
+
+  level_files_.push_back(f2);
+  level_files_.push_back(f3);
+  level_files_.push_back(f1);
+  compaction_files_.push_back(f1);
 
-int main(int argc, char** argv) {
-  return leveldb::test::RunAllTests();
+  AddBoundaryInputs(icmp_, level_files_, &compaction_files_);
+  ASSERT_EQ(3, compaction_files_.size());
+  ASSERT_EQ(f1, compaction_files_[0]);
+  ASSERT_EQ(f3, compaction_files_[1]);
+  ASSERT_EQ(f2, compaction_files_[2]);
 }
+
+TEST(AddBoundaryInputsTest, TestDisjoinFilePointers) {
+  FileMetaData* f1 =
+      CreateFileMetaData(1, InternalKey("100", 6, kTypeValue),
+                         InternalKey(InternalKey("100", 5, kTypeValue)));
+  FileMetaData* f2 =
+      CreateFileMetaData(1, InternalKey("100", 6, kTypeValue),
+                         InternalKey(InternalKey("100", 5, kTypeValue)));
+  FileMetaData* f3 =
+      CreateFileMetaData(1, InternalKey("100", 2, kTypeValue),
+                         InternalKey(InternalKey("300", 1, kTypeValue)));
+  FileMetaData* f4 =
+      CreateFileMetaData(1, InternalKey("100", 4, kTypeValue),
+                         InternalKey(InternalKey("100", 3, kTypeValue)));
+
+  level_files_.push_back(f2);
+  level_files_.push_back(f3);
+  level_files_.push_back(f4);
+
+  compaction_files_.push_back(f1);
+
+  AddBoundaryInputs(icmp_, level_files_, &compaction_files_);
+  ASSERT_EQ(3, compaction_files_.size());
+  ASSERT_EQ(f1, compaction_files_[0]);
+  ASSERT_EQ(f4, compaction_files_[1]);
+  ASSERT_EQ(f3, compaction_files_[2]);
+}
+
+}  // namespace leveldb
+
+int main(int argc, char** argv) { return leveldb::test::RunAllTests(); }
diff --git a/db/write_batch.cc b/db/write_batch.cc
index 33f4a42..b54313c 100644
--- a/db/write_batch.cc
+++ b/db/write_batch.cc
@@ -15,10 +15,10 @@
 
 #include "leveldb/write_batch.h"
 
-#include "leveldb/db.h"
 #include "db/dbformat.h"
 #include "db/memtable.h"
 #include "db/write_batch_internal.h"
+#include "leveldb/db.h"
 #include "util/coding.h"
 
 namespace leveldb {
@@ -26,19 +26,19 @@ namespace leveldb {
 // WriteBatch header has an 8-byte sequence number followed by a 4-byte count.
 static const size_t kHeader = 12;
 
-WriteBatch::WriteBatch() {
-  Clear();
-}
+WriteBatch::WriteBatch() { Clear(); }
 
-WriteBatch::~WriteBatch() { }
+WriteBatch::~WriteBatch() = default;
 
-WriteBatch::Handler::~Handler() { }
+WriteBatch::Handler::~Handler() = default;
 
 void WriteBatch::Clear() {
   rep_.clear();
   rep_.resize(kHeader);
 }
 
+size_t WriteBatch::ApproximateSize() const { return rep_.size(); }
+
 Status WriteBatch::Iterate(Handler* handler) const {
   Slice input(rep_);
   if (input.size() < kHeader) {
@@ -108,25 +108,28 @@ void WriteBatch::Delete(const Slice& key) {
   PutLengthPrefixedSlice(&rep_, key);
 }
 
+void WriteBatch::Append(const WriteBatch& source) {
+  WriteBatchInternal::Append(this, &source);
+}
+
 namespace {
 class MemTableInserter : public WriteBatch::Handler {
  public:
   SequenceNumber sequence_;
   MemTable* mem_;
 
-  virtual void Put(const Slice& key, const Slice& value) {
+  void Put(const Slice& key, const Slice& value) override {
     mem_->Add(sequence_, kTypeValue, key, value);
     sequence_++;
   }
-  virtual void Delete(const Slice& key) {
+  void Delete(const Slice& key) override {
     mem_->Add(sequence_, kTypeDeletion, key, Slice());
     sequence_++;
   }
 };
 }  // namespace
 
-Status WriteBatchInternal::InsertInto(const WriteBatch* b,
-                                      MemTable* memtable) {
+Status WriteBatchInternal::InsertInto(const WriteBatch* b, MemTable* memtable) {
   MemTableInserter inserter;
   inserter.sequence_ = WriteBatchInternal::Sequence(b);
   inserter.mem_ = memtable;
diff --git a/db/write_batch_internal.h b/db/write_batch_internal.h
index 9448ef7..fce86e3 100644
--- a/db/write_batch_internal.h
+++ b/db/write_batch_internal.h
@@ -29,13 +29,9 @@ class WriteBatchInternal {
   // this batch.
   static void SetSequence(WriteBatch* batch, SequenceNumber seq);
 
-  static Slice Contents(const WriteBatch* batch) {
-    return Slice(batch->rep_);
-  }
+  static Slice Contents(const WriteBatch* batch) { return Slice(batch->rep_); }
 
-  static size_t ByteSize(const WriteBatch* batch) {
-    return batch->rep_.size();
-  }
+  static size_t ByteSize(const WriteBatch* batch) { return batch->rep_.size(); }
 
   static void SetContents(WriteBatch* batch, const Slice& contents);
 
@@ -46,5 +42,4 @@ class WriteBatchInternal {
 
 }  // namespace leveldb
 
-
 #endif  // STORAGE_LEVELDB_DB_WRITE_BATCH_INTERNAL_H_
diff --git a/db/write_batch_test.cc b/db/write_batch_test.cc
index 9064e3d..c32317f 100644
--- a/db/write_batch_test.cc
+++ b/db/write_batch_test.cc
@@ -52,7 +52,7 @@ static std::string PrintContents(WriteBatch* b) {
   return state;
 }
 
-class WriteBatchTest { };
+class WriteBatchTest {};
 
 TEST(WriteBatchTest, Empty) {
   WriteBatch batch;
@@ -68,10 +68,11 @@ TEST(WriteBatchTest, Multiple) {
   WriteBatchInternal::SetSequence(&batch, 100);
   ASSERT_EQ(100, WriteBatchInternal::Sequence(&batch));
   ASSERT_EQ(3, WriteBatchInternal::Count(&batch));
-  ASSERT_EQ("Put(baz, boo)@102"
-            "Delete(box)@101"
-            "Put(foo, bar)@100",
-            PrintContents(&batch));
+  ASSERT_EQ(
+      "Put(baz, boo)@102"
+      "Delete(box)@101"
+      "Put(foo, bar)@100",
+      PrintContents(&batch));
 }
 
 TEST(WriteBatchTest, Corruption) {
@@ -81,40 +82,56 @@ TEST(WriteBatchTest, Corruption) {
   WriteBatchInternal::SetSequence(&batch, 200);
   Slice contents = WriteBatchInternal::Contents(&batch);
   WriteBatchInternal::SetContents(&batch,
-                                  Slice(contents.data(),contents.size()-1));
-  ASSERT_EQ("Put(foo, bar)@200"
-            "ParseError()",
-            PrintContents(&batch));
+                                  Slice(contents.data(), contents.size() - 1));
+  ASSERT_EQ(
+      "Put(foo, bar)@200"
+      "ParseError()",
+      PrintContents(&batch));
 }
 
 TEST(WriteBatchTest, Append) {
   WriteBatch b1, b2;
   WriteBatchInternal::SetSequence(&b1, 200);
   WriteBatchInternal::SetSequence(&b2, 300);
-  WriteBatchInternal::Append(&b1, &b2);
-  ASSERT_EQ("",
-            PrintContents(&b1));
+  b1.Append(b2);
+  ASSERT_EQ("", PrintContents(&b1));
   b2.Put("a", "va");
-  WriteBatchInternal::Append(&b1, &b2);
-  ASSERT_EQ("Put(a, va)@200",
-            PrintContents(&b1));
+  b1.Append(b2);
+  ASSERT_EQ("Put(a, va)@200", PrintContents(&b1));
   b2.Clear();
   b2.Put("b", "vb");
-  WriteBatchInternal::Append(&b1, &b2);
-  ASSERT_EQ("Put(a, va)@200"
-            "Put(b, vb)@201",
-            PrintContents(&b1));
+  b1.Append(b2);
+  ASSERT_EQ(
+      "Put(a, va)@200"
+      "Put(b, vb)@201",
+      PrintContents(&b1));
   b2.Delete("foo");
-  WriteBatchInternal::Append(&b1, &b2);
-  ASSERT_EQ("Put(a, va)@200"
-            "Put(b, vb)@202"
-            "Put(b, vb)@201"
-            "Delete(foo)@203",
-            PrintContents(&b1));
+  b1.Append(b2);
+  ASSERT_EQ(
+      "Put(a, va)@200"
+      "Put(b, vb)@202"
+      "Put(b, vb)@201"
+      "Delete(foo)@203",
+      PrintContents(&b1));
 }
 
-}  // namespace leveldb
+TEST(WriteBatchTest, ApproximateSize) {
+  WriteBatch batch;
+  size_t empty_size = batch.ApproximateSize();
+
+  batch.Put(Slice("foo"), Slice("bar"));
+  size_t one_key_size = batch.ApproximateSize();
+  ASSERT_LT(empty_size, one_key_size);
+
+  batch.Put(Slice("baz"), Slice("boo"));
+  size_t two_keys_size = batch.ApproximateSize();
+  ASSERT_LT(one_key_size, two_keys_size);
 
-int main(int argc, char** argv) {
-  return leveldb::test::RunAllTests();
+  batch.Delete(Slice("box"));
+  size_t post_delete_size = batch.ApproximateSize();
+  ASSERT_LT(two_keys_size, post_delete_size);
 }
+
+}  // namespace leveldb
+
+int main(int argc, char** argv) { return leveldb::test::RunAllTests(); }