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// 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 "db/memtable.h"
#include "db/dbformat.h"
#include "leveldb/comparator.h"
#include "leveldb/env.h"
#include "leveldb/iterator.h"
#include "util/coding.h"
namespace leveldb {
static Slice GetLengthPrefixedSlice(const char* data) {
uint32_t len;
const char* p = data;
p = GetVarint32Ptr(p, p + 5, &len); // +5: we assume "p" is not corrupted
return Slice(p, len);
}
MemTable::MemTable(const InternalKeyComparator& cmp)
: comparator_(cmp),
table_(comparator_, &arena_) {
}
MemTable::~MemTable() {
}
size_t MemTable::ApproximateMemoryUsage() { return arena_.MemoryUsage(); }
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);
return comparator.Compare(a, b);
}
// Encode a suitable internal key target for "target" and return it.
// Uses *scratch as scratch space, and the returned pointer will point
// into this scratch space.
static const char* EncodeKey(std::string* scratch, const Slice& target) {
scratch->clear();
PutVarint32(scratch, target.size());
scratch->append(target.data(), target.size());
return scratch->data();
}
class MemTableIterator: public Iterator {
public:
explicit MemTableIterator(MemTable::Table* table) {
iter_ = new MemTable::Table::Iterator(table);
}
virtual ~MemTableIterator() { delete iter_; }
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 {
Slice key_slice = GetLengthPrefixedSlice(iter_->key());
return GetLengthPrefixedSlice(key_slice.data() + key_slice.size());
}
virtual Status status() const { 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&);
};
Iterator* MemTable::NewIterator() {
return new MemTableIterator(&table_);
}
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()
// key bytes : char[internal_key.size()]
// value_size : varint32 of value.size()
// value bytes : char[value.size()]
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;
char* buf = arena_.Allocate(encoded_len);
char* p = EncodeVarint32(buf, internal_key_size);
memcpy(p, key.data(), key_size);
p += key_size;
EncodeFixed64(p, (s << 8) | type);
p += 8;
p = EncodeVarint32(p, val_size);
memcpy(p, value.data(), val_size);
assert((p + val_size) - buf == encoded_len);
table_.Insert(buf);
}
}
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