SERVER-34459 Clear in-memory database versions on setFCV downgrade on shard primaries and secondaries

3 files changed, 58 insertions, 30 deletions

diff --git a/src/mongo/db/commands/feature_compatibility_version.cpp b/src/mongo/db/commands/feature_compatibility_version.cpp
index 2216c24dd6d..932f8d29553 100644
--- a/src/mongo/db/commands/feature_compatibility_version.cpp
+++ b/src/mongo/db/commands/feature_compatibility_version.cpp
@@ -33,6 +33,7 @@
 #include "mongo/db/commands/feature_compatibility_version.h"
 
 #include "mongo/base/status.h"
+#include "mongo/db/catalog_raii.h"
 #include "mongo/db/commands/feature_compatibility_version_documentation.h"
 #include "mongo/db/commands/feature_compatibility_version_parser.h"
 #include "mongo/db/dbdirectclient.h"
@@ -41,6 +42,7 @@
 #include "mongo/db/operation_context.h"
 #include "mongo/db/repl/optime.h"
 #include "mongo/db/repl/storage_interface.h"
+#include "mongo/db/s/database_sharding_state.h"
 #include "mongo/db/server_parameters.h"
 #include "mongo/db/service_context.h"
 #include "mongo/db/storage/storage_engine.h"
@@ -154,12 +156,30 @@ void FeatureCompatibilityVersion::onInsertOrUpdate(OperationContext* opCtx, cons
               << FeatureCompatibilityVersionParser::toString(newVersion);
     }
 
-    // On commit, update the server parameters, close any connections with a wire version that is
-    // below the minimum, and abort any open transactions if downgrading.
     opCtx->recoveryUnit()->onCommit([opCtx, newVersion]() {
         serverGlobalParams.featureCompatibility.setVersion(newVersion);
         updateMinWireVersion();
 
+        if (newVersion == ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36) {
+            // Clear the in-memory cached database versions on downgrade, so that we do not check
+            // databaseVersion in FCV 3.6 (it would be meaningless, since databases do not have
+            // versions in FCV 3.6).
+            // TODO: Once SERVER-34431 goes in, just clear the DatabaseShardingStateMap.
+            std::vector<std::string> dbNames;
+            getGlobalServiceContext()->getGlobalStorageEngine()->listDatabases(&dbNames);
+            for (const auto& dbName : dbNames) {
+                if (dbName == "admin") {
+                    // The 'admin' database is already locked, since the FCV document is in
+                    // admin.system.version. Just skip 'admin', since it is not versioned.
+                    continue;
+                }
+                AutoGetDb autoDb(opCtx, dbName, MODE_X);
+                if (autoDb.getDb()) {
+                    DatabaseShardingState::get(autoDb.getDb()).setDbVersion(opCtx, boost::none);
+                }
+            }
+        }
+
         if (newVersion != ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo36) {
             // Close all incoming connections from internal clients with binary versions lower than
             // ours.
diff --git a/src/mongo/db/s/SConscript b/src/mongo/db/s/SConscript
index 6c43720e075..0c3d7918cb6 100644
--- a/src/mongo/db/s/SConscript
+++ b/src/mongo/db/s/SConscript
@@ -55,6 +55,7 @@ env.Library(
         'split_vector.cpp',
     ],
     LIBDEPS=[
+        '$BUILD_DIR/mongo/db/commands/mongod_fcv',
         '$BUILD_DIR/mongo/db/db_raii',
         '$BUILD_DIR/mongo/db/dbhelpers',
         '$BUILD_DIR/mongo/db/repl/oplog',
diff --git a/src/mongo/db/s/shard_filtering_metadata_refresh.cpp b/src/mongo/db/s/shard_filtering_metadata_refresh.cpp
index e641d43578e..cc3e9533ecb 100644
--- a/src/mongo/db/s/shard_filtering_metadata_refresh.cpp
+++ b/src/mongo/db/s/shard_filtering_metadata_refresh.cpp
@@ -34,6 +34,7 @@
 
 #include "mongo/db/catalog/database_holder.h"
 #include "mongo/db/catalog_raii.h"
+#include "mongo/db/commands/feature_compatibility_version.h"
 #include "mongo/db/operation_context.h"
 #include "mongo/db/s/collection_sharding_state.h"
 #include "mongo/db/s/database_sharding_state.h"
@@ -200,13 +201,39 @@ void forceDatabaseRefresh(OperationContext* opCtx, const StringData dbName) {
         uassertStatusOK(Grid::get(opCtx)->catalogCache()->getDatabaseWithRefresh(opCtx, dbName))
             .databaseVersion();
 
-    // First, check under a shared lock if another thread already updated the cached version.
-    // This is a best-effort optimization to make as few threads as possible to convoy on the
-    // exclusive lock below.
-    {
-        // Take the DBLock directly rather than using AutoGetDb, to prevent a recursive call
-        // into checkDbVersion().
-        Lock::DBLock dbLock(opCtx, dbName, MODE_IS);
+    // Only set the in-memory version in FCV 4.0, and hold the lock across checking the FCV and
+    // setting the version.
+    Lock::SharedLock lk(opCtx->lockState(), FeatureCompatibilityVersion::fcvLock);
+    if (serverGlobalParams.featureCompatibility.getVersion() ==
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo40) {
+        // First, check under a shared lock if another thread already updated the cached version.
+        // This is a best-effort optimization to make as few threads as possible to convoy on the
+        // exclusive lock below.
+        {
+            // Take the DBLock directly rather than using AutoGetDb, to prevent a recursive call
+            // into checkDbVersion().
+            Lock::DBLock dbLock(opCtx, dbName, MODE_IS);
+            const auto db = dbHolder().get(opCtx, dbName);
+            if (!db) {
+                log() << "Database " << dbName
+                      << " has been dropped; not caching the refreshed databaseVersion";
+                return;
+            }
+
+            const auto cachedDbVersion = DatabaseShardingState::get(db).getDbVersion(opCtx);
+            if (cachedDbVersion && refreshedDbVersion &&
+                cachedDbVersion->getUuid() == refreshedDbVersion->getUuid() &&
+                cachedDbVersion->getLastMod() >= refreshedDbVersion->getLastMod()) {
+                LOG(2) << "Skipping setting cached databaseVersion for " << dbName
+                       << " to refreshed version " << refreshedDbVersion->toBSON()
+                       << " because current cached databaseVersion is already "
+                       << cachedDbVersion->toBSON();
+                return;
+            }
+        }
+
+        // The cached version is older than the refreshed version; update the cached version.
+        Lock::DBLock dbLock(opCtx, dbName, MODE_X);
         const auto db = dbHolder().get(opCtx, dbName);
         if (!db) {
             log() << "Database " << dbName
@@ -214,28 +241,8 @@ void forceDatabaseRefresh(OperationContext* opCtx, const StringData dbName) {
             return;
         }
 
-        const auto cachedDbVersion = DatabaseShardingState::get(db).getDbVersion(opCtx);
-        if (cachedDbVersion && refreshedDbVersion &&
-            cachedDbVersion->getUuid() == refreshedDbVersion->getUuid() &&
-            cachedDbVersion->getLastMod() >= refreshedDbVersion->getLastMod()) {
-            LOG(2) << "Skipping setting cached databaseVersion for " << dbName
-                   << " to refreshed version " << refreshedDbVersion->toBSON()
-                   << " because current cached databaseVersion is already "
-                   << cachedDbVersion->toBSON();
-            return;
-        }
+        DatabaseShardingState::get(db).setDbVersion(opCtx, std::move(refreshedDbVersion));
     }
-
-    // The cached version is older than the refreshed version; update the cached version.
-    Lock::DBLock dbLock(opCtx, dbName, MODE_X);
-    const auto db = dbHolder().get(opCtx, dbName);
-    if (!db) {
-        log() << "Database " << dbName
-              << " has been dropped; not caching the refreshed databaseVersion";
-        return;
-    }
-
-    DatabaseShardingState::get(db).setDbVersion(opCtx, std::move(refreshedDbVersion));
 }
 
 }  // namespace mongo