SERVER-48990 Added comparable chunk version as a prerequisite to implement a causally consistent collection cache

4 files changed, 214 insertions, 1 deletions

diff --git a/src/mongo/s/SConscript b/src/mongo/s/SConscript
index 771a567dc7b..ef829350aeb 100644
--- a/src/mongo/s/SConscript
+++ b/src/mongo/s/SConscript
@@ -570,6 +570,7 @@ env.CppUnitTest(
         'build_versioned_requests_for_targeted_shards_test.cpp',
         'catalog_cache_test.cpp',
         'catalog_cache_refresh_test.cpp',
+        'comparable_chunk_version_test.cpp',
         'comparable_database_version_test.cpp',
         'catalog/type_changelog_test.cpp',
         'catalog/type_chunk_test.cpp',
diff --git a/src/mongo/s/catalog_cache.cpp b/src/mongo/s/catalog_cache.cpp
index 0d0c0bdbad4..6ed5ed4ce90 100644
--- a/src/mongo/s/catalog_cache.cpp
+++ b/src/mongo/s/catalog_cache.cpp
@@ -861,6 +861,32 @@ DatabaseVersion CachedDatabaseInfo::databaseVersion() const {
     return _dbt.getVersion();
 }
 
+AtomicWord<uint64_t> ComparableChunkVersion::_localSequenceNumSource{1ULL};
+
+ComparableChunkVersion ComparableChunkVersion::makeComparableChunkVersion(
+    const ChunkVersion& version) {
+    return ComparableChunkVersion(version, _localSequenceNumSource.fetchAndAdd(1));
+}
+
+const ChunkVersion& ComparableChunkVersion::getVersion() const {
+    return _chunkVersion;
+}
+
+uint64_t ComparableChunkVersion::getLocalSequenceNum() const {
+    return _localSequenceNum;
+}
+
+BSONObj ComparableChunkVersion::toBSON() const {
+    BSONObjBuilder builder;
+    _chunkVersion.appendToCommand(&builder);
+    builder.append("localSequenceNum", std::to_string(_localSequenceNum));
+    return builder.obj();
+}
+
+std::string ComparableChunkVersion::toString() const {
+    return toBSON().toString();
+}
+
 CachedCollectionRoutingInfo::CachedCollectionRoutingInfo(NamespaceString nss,
                                                          CachedDatabaseInfo db,
                                                          std::shared_ptr<ChunkManager> cm)
diff --git a/src/mongo/s/catalog_cache.h b/src/mongo/s/catalog_cache.h
index b699cb0d5ac..3a98d31826d 100644
--- a/src/mongo/s/catalog_cache.h
+++ b/src/mongo/s/catalog_cache.h
@@ -37,6 +37,7 @@
 #include "mongo/s/catalog/type_database.h"
 #include "mongo/s/catalog_cache_loader.h"
 #include "mongo/s/chunk_manager.h"
+#include "mongo/s/chunk_version.h"
 #include "mongo/s/client/shard.h"
 #include "mongo/s/database_version_gen.h"
 #include "mongo/util/concurrency/notification.h"
@@ -144,7 +145,83 @@ private:
 
     DatabaseVersion _dbVersion;
     // Locally incremented sequence number that allows to compare two database versions with
-    // different UUIDs. Each new comparableDatabaseVersion will have a grater sequence number then
+    // different UUIDs. Each new comparableDatabaseVersion will have a greater sequence number then
+    // the ones created before.
+    uint64_t _localSequenceNum{0};
+};
+
+/**
+ * Constructed to be used exclusively by the CatalogCache as a vector clock (Time) to drive
+ * CollectionCache's lookups.
+ *
+ * The ChunkVersion class contains an non comparable epoch, which makes impossible to compare two
+ * ChunkVersions when their epochs's differ.
+ *
+ * This class wraps a ChunkVersion object with a node-local sequence number (_localSequenceNum) that
+ * allows the comparision.
+ *
+ * This class should go away once a cluster-wide comparable ChunkVersion is implemented.
+ */
+class ComparableChunkVersion {
+public:
+    static ComparableChunkVersion makeComparableChunkVersion(const ChunkVersion& version);
+
+    ComparableChunkVersion() = default;
+
+    const ChunkVersion& getVersion() const;
+
+    uint64_t getLocalSequenceNum() const;
+
+    BSONObj toBSON() const;
+
+    std::string toString() const;
+
+    bool sameEpoch(const ComparableChunkVersion& other) const {
+        return _chunkVersion.epoch() == other._chunkVersion.epoch();
+    }
+
+    bool operator==(const ComparableChunkVersion& other) const {
+        return sameEpoch(other) &&
+            (_chunkVersion.majorVersion() == other._chunkVersion.majorVersion() &&
+             _chunkVersion.minorVersion() == other._chunkVersion.minorVersion());
+    }
+
+    bool operator!=(const ComparableChunkVersion& other) const {
+        return !(*this == other);
+    }
+
+    bool operator<(const ComparableChunkVersion& other) const {
+        if (sameEpoch(other)) {
+            return _chunkVersion.majorVersion() < other._chunkVersion.majorVersion() ||
+                (_chunkVersion.majorVersion() == other._chunkVersion.majorVersion() &&
+                 _chunkVersion.minorVersion() < other._chunkVersion.minorVersion());
+        } else {
+            return _localSequenceNum < other._localSequenceNum;
+        }
+    }
+
+    bool operator>(const ComparableChunkVersion& other) const {
+        return other < *this;
+    }
+
+    bool operator<=(const ComparableChunkVersion& other) const {
+        return !(*this > other);
+    }
+
+    bool operator>=(const ComparableChunkVersion& other) const {
+        return !(*this < other);
+    }
+
+private:
+    static AtomicWord<uint64_t> _localSequenceNumSource;
+
+    ComparableChunkVersion(const ChunkVersion& version, uint64_t localSequenceNum)
+        : _chunkVersion(version), _localSequenceNum(localSequenceNum) {}
+
+    ChunkVersion _chunkVersion;
+
+    // Locally incremented sequence number that allows to compare two colection versions with
+    // different epochs. Each new comparableChunkVersion will have a greater sequence number than
     // the ones created before.
     uint64_t _localSequenceNum{0};
 };
diff --git a/src/mongo/s/comparable_chunk_version_test.cpp b/src/mongo/s/comparable_chunk_version_test.cpp
new file mode 100644
index 00000000000..941d9bad080
--- /dev/null
+++ b/src/mongo/s/comparable_chunk_version_test.cpp
@@ -0,0 +1,109 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/s/catalog_cache.h"
+#include "mongo/s/chunk_version.h"
+#include "mongo/unittest/unittest.h"
+
+namespace mongo {
+namespace {
+
+TEST(ComparableChunkVersionTest, VersionsEqual) {
+    auto epoch = OID::gen();
+    const auto version1 =
+        ComparableChunkVersion::makeComparableChunkVersion(ChunkVersion(1, 0, epoch));
+    const auto version2 =
+        ComparableChunkVersion::makeComparableChunkVersion(ChunkVersion(1, 0, epoch));
+    ASSERT(version1.getVersion() == version2.getVersion());
+    ASSERT(version1 == version2);
+}
+
+TEST(ComparableChunkVersionTest, VersionsEqualAfterCopy) {
+    ChunkVersion chunkVersion(1, 0, OID::gen());
+    const auto version1 = ComparableChunkVersion::makeComparableChunkVersion(chunkVersion);
+    const auto version2 = version1;
+    ASSERT(version1 == version2);
+}
+
+TEST(ComparableChunkVersionTest, CompareVersionDifferentEpochs) {
+    const auto version1 =
+        ComparableChunkVersion::makeComparableChunkVersion(ChunkVersion(2, 0, OID::gen()));
+    const auto version2 =
+        ComparableChunkVersion::makeComparableChunkVersion(ChunkVersion(1, 0, OID::gen()));
+    ASSERT(version2 != version1);
+    ASSERT(version2 > version1);
+    ASSERT_FALSE(version2 < version1);
+}
+
+TEST(ComparableChunkVersionTest, VersionGreaterSameEpochs) {
+    const auto epoch = OID::gen();
+    const auto version1 =
+        ComparableChunkVersion::makeComparableChunkVersion(ChunkVersion(1, 0, epoch));
+    const auto version2 =
+        ComparableChunkVersion::makeComparableChunkVersion(ChunkVersion(1, 1, epoch));
+    const auto version3 =
+        ComparableChunkVersion::makeComparableChunkVersion(ChunkVersion(2, 0, epoch));
+    ASSERT(version2 != version1);
+    ASSERT(version2 > version1);
+    ASSERT_FALSE(version2 < version1);
+    ASSERT(version3 != version2);
+    ASSERT(version3 > version2);
+    ASSERT_FALSE(version3 < version2);
+}
+
+TEST(ComparableChunkVersionTest, VersionLessSameEpoch) {
+    const auto epoch = OID::gen();
+    const auto version1 =
+        ComparableChunkVersion::makeComparableChunkVersion(ChunkVersion(1, 0, epoch));
+    const auto version2 =
+        ComparableChunkVersion::makeComparableChunkVersion(ChunkVersion(1, 1, epoch));
+    const auto version3 =
+        ComparableChunkVersion::makeComparableChunkVersion(ChunkVersion(2, 0, epoch));
+    ASSERT(version1 != version2);
+    ASSERT(version1 < version2);
+    ASSERT_FALSE(version1 > version2);
+    ASSERT(version3 != version2);
+    ASSERT(version2 < version3);
+    ASSERT_FALSE(version2 > version3);
+}
+
+TEST(ComparableChunkVersionTest, DefaultConstructedVersionIsAlwaysLess) {
+    const ComparableChunkVersion defaultVersion{};
+    ASSERT_EQ(defaultVersion.getLocalSequenceNum(), 0);
+    const auto version1 =
+        ComparableChunkVersion::makeComparableChunkVersion(ChunkVersion(0, 0, OID::gen()));
+    ASSERT(defaultVersion != version1);
+    ASSERT(defaultVersion < version1);
+    ASSERT_FALSE(defaultVersion > version1);
+}
+
+}  // namespace
+}  // namespace mongo