SERVER-69108 SCCL can immediately return config and admin metadata without triggering a refresh

3 files changed, 57 insertions, 0 deletions

diff --git a/src/mongo/db/s/flush_database_cache_updates_command.cpp b/src/mongo/db/s/flush_database_cache_updates_command.cpp
index cf4a033f668..39c24528a40 100644
--- a/src/mongo/db/s/flush_database_cache_updates_command.cpp
+++ b/src/mongo/db/s/flush_database_cache_updates_command.cpp
@@ -38,6 +38,7 @@
 #include "mongo/db/catalog_raii.h"
 #include "mongo/db/client.h"
 #include "mongo/db/commands.h"
+#include "mongo/db/dbdirectclient.h"
 #include "mongo/db/operation_context.h"
 #include "mongo/db/repl/repl_client_info.h"
 #include "mongo/db/s/database_sharding_state.h"
@@ -55,6 +56,30 @@
 namespace mongo {
 namespace {
 
+/**
+ * Inserts a database collection entry with fixed metadata for the `config` or `admin` database. If
+ * the entry key already exists, it's not updated.
+ */
+Status insertDatabaseEntryForBackwardCompatibility(OperationContext* opCtx,
+                                                   const StringData& dbName) {
+    invariant(dbName == NamespaceString::kAdminDb || dbName == NamespaceString::kConfigDb);
+
+    DBDirectClient client(opCtx);
+    auto commandResponse = client.runCommand([&] {
+        auto dbMetadata = DatabaseType(dbName.toString(),
+                                       ShardId::kConfigServerId,
+                                       dbName == NamespaceString::kConfigDb,
+                                       DatabaseVersion::makeFixed());
+
+        write_ops::InsertCommandRequest insertOp(NamespaceString::kShardConfigDatabasesNamespace);
+        insertOp.setDocuments({dbMetadata.toBSON()});
+        return insertOp.serialize({});
+    }());
+
+    auto commandStatus = getStatusFromWriteCommandReply(commandResponse->getCommandReply());
+    return commandStatus.code() == ErrorCodes::DuplicateKey ? Status::OK() : commandStatus;
+}
+
 template <typename Derived>
 class FlushDatabaseCacheUpdatesCmdBase : public TypedCommand<Derived> {
 public:
@@ -119,6 +144,26 @@ public:
                     "Can't call _flushDatabaseCacheUpdates if in read-only mode",
                     !storageGlobalParams.readOnly);
 
+            if (_dbName() == NamespaceString::kAdminDb || _dbName() == NamespaceString::kConfigDb) {
+                // The admin and config databases have fixed metadata that does not need to be
+                // refreshed.
+
+                if (Base::request().getSyncFromConfig()) {
+                    // To ensure compatibility with old secondaries that still call the
+                    // _flushDatabaseCacheUpdates command to get updated database metadata from
+                    // primary, an entry with fixed metadata is inserted in the
+                    // config.cache.databases collection.
+
+                    LOGV2_DEBUG(6910800,
+                                1,
+                                "Inserting a database collection entry with fixed metadata",
+                                "db"_attr = _dbName());
+                    uassertStatusOK(insertDatabaseEntryForBackwardCompatibility(opCtx, _dbName()));
+                }
+
+                return;
+            }
+
             auto& oss = OperationShardingState::get(opCtx);
 
             {
diff --git a/src/mongo/db/s/shard_filtering_metadata_refresh.cpp b/src/mongo/db/s/shard_filtering_metadata_refresh.cpp
index c00d00ff670..9d4936a9c82 100644
--- a/src/mongo/db/s/shard_filtering_metadata_refresh.cpp
+++ b/src/mongo/db/s/shard_filtering_metadata_refresh.cpp
@@ -67,6 +67,10 @@ void onDbVersionMismatch(OperationContext* opCtx,
 
     invariant(ShardingState::get(opCtx)->canAcceptShardedCommands());
 
+    tassert(ErrorCodes::IllegalOperation,
+            "Can't check version of {} database"_format(dbName),
+            dbName != NamespaceString::kAdminDb && dbName != NamespaceString::kConfigDb);
+
     if (serverDbVersion) {
         // Do not reorder these two statements! if the comparison is done through epochs, the
         // construction order matters: we are pessimistically assuming that the client version
diff --git a/src/mongo/db/s/shard_server_catalog_cache_loader.cpp b/src/mongo/db/s/shard_server_catalog_cache_loader.cpp
index 2f7dc1e180b..b171b3689bf 100644
--- a/src/mongo/db/s/shard_server_catalog_cache_loader.cpp
+++ b/src/mongo/db/s/shard_server_catalog_cache_loader.cpp
@@ -498,6 +498,14 @@ SemiFuture<CollectionAndChangedChunks> ShardServerCatalogCacheLoader::getChunksS
 }
 
 SemiFuture<DatabaseType> ShardServerCatalogCacheLoader::getDatabase(StringData dbName) {
+    // The admin and config database have fixed metadata that does not need to be refreshed.
+    if (dbName == NamespaceString::kAdminDb || dbName == NamespaceString::kConfigDb) {
+        return DatabaseType(dbName.toString(),
+                            ShardId::kConfigServerId,
+                            dbName == NamespaceString::kConfigDb,
+                            DatabaseVersion::makeFixed());
+    }
+
     const auto [isPrimary, term] = [&] {
         stdx::lock_guard<Latch> lock(_mutex);
         return std::make_tuple(_role == ReplicaSetRole::Primary, _term);