Validate relation name before logging it

src/backend/distributed/operations/shard_split.c

@@ -79,6 +79,8 @@ static void CreateAndCopySplitShardsForShardGroup(WorkerNode *sourceShardNode,
 												  List *sourceColocatedShardIntervalList,
 												  List *shardGroupSplitIntervalListList,
 												  List *workersForPlacementList);
+static bool CheckIfRelationWithSameNameExists(ShardInterval *shardInterval,
+										   WorkerNode *workerNode);
 static void CreateSplitShardsForShardGroup(List *shardGroupSplitIntervalListList,
 										   List *workersForPlacementList);
 static void CreateDummyShardsForShardGroup(HTAB *mapOfPlacementToDummyShardList,
@@ -548,6 +550,55 @@ BlockingShardSplit(SplitOperation splitOperation,
 }
 
 
+/* Check if a relation with given name already exists on the worker node */
+static bool
+CheckIfRelationWithSameNameExists(ShardInterval *shardInterval, WorkerNode *workerNode)
+{
+	char *schemaName = get_namespace_name(
+		get_rel_namespace(shardInterval->relationId));
+	char *shardName = get_rel_name(shardInterval->relationId);
+	AppendShardIdToName(&shardName, shardInterval->shardId);
+
+	StringInfo checkShardExistsQuery = makeStringInfo();
+	appendStringInfo(checkShardExistsQuery,
+					 "SELECT EXISTS (SELECT FROM pg_tables WHERE schemaname = '%s' AND tablename = '%s');",
+					 schemaName,
+					 shardName);
+
+	int connectionFlags = 0;
+	MultiConnection *connection = GetNodeUserDatabaseConnection(connectionFlags,
+																workerNode->workerName,
+																workerNode->workerPort,
+																CitusExtensionOwnerName(),
+																get_database_name(
+																	MyDatabaseId));
+
+	PGresult *result = NULL;
+	int queryResult = ExecuteOptionalRemoteCommand(connection,
+												   checkShardExistsQuery->data, &result);
+	if (queryResult != RESPONSE_OKAY || !IsResponseOK(result) || PQntuples(result) != 1)
+	{
+		ereport(ERROR, (errcode(ERRCODE_CONNECTION_FAILURE),
+						errmsg(
+							"Cannot check if relation %s already exists for split on worker %s:%d",
+							ConstructQualifiedShardName(shardInterval),
+							connection->hostname,
+							connection->port)));
+
+		PQclear(result);
+		ForgetResults(connection);
+
+		return false;
+	}
+
+	char *checkExists = PQgetvalue(result, 0, 0);
+	PQclear(result);
+	ForgetResults(connection);
+
+	return strcmp(checkExists, "t") == 0;
+}
+
+
 /* Create ShardGroup split children on a list of corresponding workers. */
 static void
 CreateSplitShardsForShardGroup(List *shardGroupSplitIntervalListList,
@@ -578,7 +629,24 @@ CreateSplitShardsForShardGroup(List *shardGroupSplitIntervalListList,
 				splitShardCreationCommandList,
 				shardInterval->shardId);
 
-			/* Log resource for cleanup in case of failure only. */
+			/* Log resource for cleanup in case of failure only.
+			 * Before we log a record, do a best effort check to see if a shard with same name exists.
+			 * This is because, it will cause shard creation to fail and we will end up cleaning the
+			 * old shard. We don't want that.
+			 */
+			bool relationExists = CheckIfRelationWithSameNameExists(shardInterval,
+															  workerPlacementNode);
+
+			if (relationExists)
+			{
+				ereport(ERROR, (errcode(ERRCODE_DUPLICATE_TABLE),
+								errmsg("Relation %s already exists on worker %s:%d.",
+									   ConstructQualifiedShardName(shardInterval),
+									   workerPlacementNode->workerName,
+									   workerPlacementNode->workerPort)));
+			}
+			else
+			{
 				CleanupPolicy policy = CLEANUP_ON_FAILURE;
 				InsertCleanupRecordInSubtransaction(CLEANUP_SHARD_PLACEMENT,
 													ConstructQualifiedShardName(
@@ -587,7 +655,9 @@ CreateSplitShardsForShardGroup(List *shardGroupSplitIntervalListList,
 													policy);
 
 				/* Create new split child shard on the specified placement list */
-			CreateObjectOnPlacement(splitShardCreationCommandList, workerPlacementNode);
+				CreateObjectOnPlacement(splitShardCreationCommandList,
+										workerPlacementNode);
+			}
 		}
 	}
 }
@@ -1459,6 +1529,24 @@ CreateDummyShardsForShardGroup(HTAB *mapOfPlacementToDummyShardList,
 				splitShardCreationCommandList,
 				shardInterval->shardId);
 
+			/* Log resource for cleanup in case of failure only.
+			 * Before we log a record, do a best effort check to see if a shard with same name exists.
+			 * This is because, it will cause shard creation to fail and we will end up cleaning the
+			 * old shard. We don't want that.
+			 */
+			bool relationExists = CheckIfRelationWithSameNameExists(shardInterval,
+															  workerPlacementNode);
+
+			if (relationExists)
+			{
+				ereport(ERROR, (errcode(ERRCODE_DUPLICATE_TABLE),
+								errmsg("Relation %s already exists on worker %s:%d.",
+									   ConstructQualifiedShardName(shardInterval),
+									   workerPlacementNode->workerName,
+									   workerPlacementNode->workerPort)));
+			}
+			else
+			{
 				/* Log shard in pg_dist_cleanup. Given dummy shards are transient resources,
 				 * we want to cleanup irrespective of operation success or failure.
 				 */
@@ -1470,7 +1558,8 @@ CreateDummyShardsForShardGroup(HTAB *mapOfPlacementToDummyShardList,
 													policy);
 
 				/* Create dummy source shard on the specified placement list */
-			CreateObjectOnPlacement(splitShardCreationCommandList, workerPlacementNode);
+				CreateObjectOnPlacement(splitShardCreationCommandList,
+										workerPlacementNode);
 
 				/* Add dummy source shard entry created for placement node in map */
 				AddDummyShardEntryInMap(mapOfPlacementToDummyShardList,
@@ -1478,6 +1567,7 @@ CreateDummyShardsForShardGroup(HTAB *mapOfPlacementToDummyShardList,
 										shardInterval);
 			}
 		}
+	}
 
 	/*
 	 * Statisfy Constraint 2: Create dummy target shards from shard group on source node.
@@ -1504,6 +1594,24 @@ CreateDummyShardsForShardGroup(HTAB *mapOfPlacementToDummyShardList,
 				splitShardCreationCommandList,
 				shardInterval->shardId);
 
+			/* Log resource for cleanup in case of failure only.
+			 * Before we log a record, do a best effort check to see if a shard with same name exists.
+			 * This is because, it will cause shard creation to fail and we will end up cleaning the
+			 * old shard. We don't want that.
+			 */
+			bool relationExists = CheckIfRelationWithSameNameExists(shardInterval,
+															  sourceWorkerNode);
+
+			if (relationExists)
+			{
+				ereport(ERROR, (errcode(ERRCODE_DUPLICATE_TABLE),
+								errmsg("Relation %s already exists on worker %s:%d.",
+									   ConstructQualifiedShardName(shardInterval),
+									   sourceWorkerNode->workerName,
+									   sourceWorkerNode->workerPort)));
+			}
+			else
+			{
 				/* Log shard in pg_dist_cleanup. Given dummy shards are transient resources,
 				 * we want to cleanup irrespective of operation success or failure.
 				 */
@@ -1523,6 +1631,7 @@ CreateDummyShardsForShardGroup(HTAB *mapOfPlacementToDummyShardList,
 										shardInterval);
 			}
 		}
+	}
 }
 
 

src/test/regress/expected/citus_split_shard_by_split_points_failure.out

@@ -72,8 +72,7 @@ SELECT pg_catalog.citus_split_shard_by_split_points(
     ARRAY['-1073741824'],
     ARRAY[:worker_1_node, :worker_1_node],
     'block_writes');
-ERROR:  relation "sensors_8981002" already exists
+ERROR:  Relation citus_split_failure_test_schema.sensors_8981002 already exists on worker localhost:xxxxx.
-CONTEXT:  while executing command on localhost:xxxxx
 -- BEGIN : Split Shard, which is expected to fail.
 -- BEGIN : Ensure tables were cleaned from worker
 \c - - - :worker_1_port