Revert "Revert "SERVER-32983 persist a version field in new config.databases entries in fcv>=4.0""

This reverts commit d7c127cb2c.

buildscripts/resmokeconfig/suites/sharding_last_stable_mongos_and_mixed_shards.yml

@@ -19,6 +19,7 @@ selector:
   # 3.6 becomes 'last-stable'.
   - jstests/sharding/covered_shard_key_indexes.js
   # Enable when 3.8 becomes last-stable.
+  - jstests/sharding/create_database.js
   - jstests/sharding/dump_coll_metadata.js
   - jstests/sharding/geo_near_random1.js
   - jstests/sharding/geo_near_random2.js

jstests/sharding/create_database.js

@@ -0,0 +1,79 @@
+/**
+ * Tests that creating a database causes it to be written to the sharding catalog with a
+ * databaseVersion if FCV > 3.6, but not if FCV <= 3.6.
+ */
+(function() {
+    'use strict';
+
+    function createDatabase(st, dbName) {
+        // A database is implicitly created when a collection inside it is created.
+        assert.commandWorked(st.s.getDB(dbName).runCommand({create: collName}));
+    }
+
+    function cleanUp(st, dbName) {
+        assert.commandWorked(st.s.getDB(dbName).runCommand({dropDatabase: 1}));
+    }
+
+    function assertHasDbVersion(dbEntry) {
+        assert.neq(null, dbEntry);
+        assert.neq(null, dbEntry.version);
+        assert.neq(null, dbEntry.version.uuid);
+        assert.eq(1, dbEntry.version.lastMod);
+    }
+
+    function assertDoesntHaveDbVersion(dbEntry) {
+        assert.neq(null, dbEntry);
+        assert.eq(null, dbEntry.version);
+    }
+
+    const dbName = "db1";
+    const collName = "foo";
+
+    var st = new ShardingTest({shards: 1});
+
+    let dbEntry;
+
+    //
+    // FCV 4.0
+    //
+
+    assert.commandWorked(st.s.adminCommand({setFeatureCompatibilityVersion: "4.0"}));
+
+    // A new database is given a databaseVersion.
+    createDatabase(st, dbName);
+    let dbEntry1 = st.s.getDB("config").getCollection("databases").findOne({_id: dbName});
+    assertHasDbVersion(dbEntry1);
+    cleanUp(st, dbName);
+
+    // A new incarnation of a database that was previously dropped is given a fresh databaseVersion.
+    createDatabase(st, dbName);
+    let dbEntry2 = st.s.getDB("config").getCollection("databases").findOne({_id: dbName});
+    assertHasDbVersion(dbEntry2);
+    assert.neq(dbEntry1.version.uuid, dbEntry2.version.uuid);
+    cleanUp(st, dbName);
+
+    //
+    // FCV 3.6
+    //
+
+    assert.commandWorked(st.s.adminCommand({setFeatureCompatibilityVersion: "3.6"}));
+
+    // A new database is not given a databaseVersion.
+    createDatabase(st, dbName);
+    dbEntry = st.s.getDB("config").getCollection("databases").findOne({_id: dbName});
+    assertDoesntHaveDbVersion(dbEntry);
+    cleanUp(st, dbName);
+
+    //
+    // FCV 3.4 (This section can be deleted once FCV 3.4 is removed).
+    //
+
+    assert.commandWorked(st.s.adminCommand({setFeatureCompatibilityVersion: "3.4"}));
+
+    // A new database is not given a databaseVersion.
+    createDatabase(st, dbName);
+    dbEntry = st.s.getDB("config").getCollection("databases").findOne({_id: dbName});
+    assertDoesntHaveDbVersion(dbEntry);
+    cleanUp(st, dbName);
+
+})();

src/mongo/db/s/config/sharding_catalog_manager_database_operations.cpp

@@ -33,12 +33,15 @@
 #include <pcrecpp.h>
 
 #include "mongo/bson/util/bson_extract.h"
+#include "mongo/db/commands/feature_compatibility_version.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/repl/repl_client_info.h"
+#include "mongo/db/server_options.h"
 #include "mongo/s/catalog/sharding_catalog_client_impl.h"
 #include "mongo/s/catalog/type_database.h"
 #include "mongo/s/client/shard.h"
 #include "mongo/s/grid.h"
+#include "mongo/s/versioning.h"
 #include "mongo/util/log.h"
 
 namespace mongo {
@@ -101,13 +104,32 @@ DatabaseType ShardingCatalogManager::createDatabase(OperationContext* opCtx,
         return uassertStatusOK(DatabaseType::fromBSON(dbObj));
     }
 
-    // The database does not exist. Pick a primary shard to place it on.
-    auto const primaryShardId =
+    // The database does not exist. Insert an entry for the new database into the sharding catalog.
+
+    // Pick a primary shard for the new database.
+    const auto primaryShardId =
         uassertStatusOK(_selectShardForNewDatabase(opCtx, Grid::get(opCtx)->shardRegistry()));
-    log() << "Placing [" << dbName << "] on: " << primaryShardId;
+
+    // Take the fcvLock to prevent the fcv from changing from the point we decide whether to include
+    // a databaseVersion until after we finish writing the database entry. Otherwise, we may end up
+    // in fcv>3.6, but without a databaseVersion.
+    invariant(!opCtx->lockState()->isLocked());
+    Lock::SharedLock lk(opCtx->lockState(), FeatureCompatibilityVersion::fcvLock);
+
+    // If in FCV>3.6, generate a databaseVersion, including a UUID, for the new database.
+    boost::optional<DatabaseVersion> dbVersion = boost::none;
+    if (serverGlobalParams.featureCompatibility.getVersion() ==
+            ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo40 ||
+        serverGlobalParams.featureCompatibility.getVersion() ==
+            ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo40) {
+        dbVersion = Versioning::newDatabaseVersion();
+    }
 
     // Insert an entry for the new database into the sharding catalog.
-    DatabaseType db(dbName, primaryShardId, false);
+    DatabaseType db(dbName, std::move(primaryShardId), false, std::move(dbVersion));
+
+    log() << "Registering new database " << db << " in sharding catalog";
+
     uassertStatusOK(Grid::get(opCtx)->catalogClient()->insertConfigDocument(
         opCtx, DatabaseType::ConfigNS, db.toBSON(), ShardingCatalogClient::kMajorityWriteConcern));
 

src/mongo/s/versioning.cpp

@@ -36,7 +36,7 @@ namespace mongo {
 
 DatabaseVersion Versioning::newDatabaseVersion() {
     DatabaseVersion dbv;
-    dbv.setLastMod(0);
+    dbv.setLastMod(1);
     dbv.setUuid(UUID::gen());
     return dbv;
 }