Fix buffer refcount leak with FDW bulk inserts

michaelpq · michaelpq · commit aa6177c882d4 · 2023-04-25T09:42:33.000+09:00
The leak would show up when using batch inserts with foreign tables included in a partition tree, as the slots used in the batch were not reset once processed. In order to fix this problem, some ExecClearTuple() are added to clean up the slots used once a batch is filled and processed, mapping with the number of slots currently in use as tracked by the counter ri_NumSlots. This buffer refcount leak has been introduced in b676ac4 with the addition of the executor facility to improve bulk inserts for FDWs, so backpatch down to 14. Alexander has provided the patch (slightly modified by me). The test for postgres_fdw comes from me, based on the test case that the author has sent in the report. Author: Alexander Pyhalov Discussion: https://postgr.es/m/b035780a740efd38dc30790c76927255@postgrespro.ru Backpatch-through: 14
diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -6867,6 +6867,28 @@ select * from grem1;
 (2 rows)
 
 delete from grem1;
+-- batch insert with foreign partitions.
+-- This schema uses two partitions, one local and one remote with a modulo
+-- to loop across all of them in batches.
+create table tab_batch_local (id int, data text);
+insert into tab_batch_local select i, 'test'|| i from generate_series(1, 45) i;
+create table tab_batch_sharded (id int, data text) partition by hash(id);
+create table tab_batch_sharded_p0 partition of tab_batch_sharded
+  for values with (modulus 2, remainder 0);
+create table tab_batch_sharded_p1_remote (id int, data text);
+create foreign table tab_batch_sharded_p1 partition of tab_batch_sharded
+  for values with (modulus 2, remainder 1)
+  server loopback options (table_name 'tab_batch_sharded_p1_remote');
+insert into tab_batch_sharded select * from tab_batch_local;
+select count(*) from tab_batch_sharded;
+ count 
+-------
+    45
+(1 row)
+
+drop table tab_batch_local;
+drop table tab_batch_sharded;
+drop table tab_batch_sharded_p1_remote;
 alter server loopback options (drop batch_size);
 -- ===================================================================
 -- test local triggers
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -1619,6 +1619,24 @@ insert into grem1 (a) values (1), (2);
 select * from gloc1;
 select * from grem1;
 delete from grem1;
+-- batch insert with foreign partitions.
+-- This schema uses two partitions, one local and one remote with a modulo
+-- to loop across all of them in batches.
+create table tab_batch_local (id int, data text);
+insert into tab_batch_local select i, 'test'|| i from generate_series(1, 45) i;
+create table tab_batch_sharded (id int, data text) partition by hash(id);
+create table tab_batch_sharded_p0 partition of tab_batch_sharded
+  for values with (modulus 2, remainder 0);
+create table tab_batch_sharded_p1_remote (id int, data text);
+create foreign table tab_batch_sharded_p1 partition of tab_batch_sharded
+  for values with (modulus 2, remainder 1)
+  server loopback options (table_name 'tab_batch_sharded_p1_remote');
+insert into tab_batch_sharded select * from tab_batch_local;
+select count(*) from tab_batch_sharded;
+drop table tab_batch_local;
+drop table tab_batch_sharded;
+drop table tab_batch_sharded_p1_remote;
+
 alter server loopback options (drop batch_size);
 
 -- ===================================================================
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
@@ -837,7 +837,6 @@ ExecInsert(ModifyTableContext *context,
 								resultRelInfo->ri_PlanSlots,
 								resultRelInfo->ri_NumSlots,
 								estate, canSetTag);
-				resultRelInfo->ri_NumSlots = 0;
 				flushed = true;
 			}
 
@@ -1240,6 +1239,14 @@ ExecBatchInsert(ModifyTableState *mtstate,
 
 	if (canSetTag && numInserted > 0)
 		estate->es_processed += numInserted;
+
+	/* Clean up all the slots, ready for the next batch */
+	for (i = 0; i < numSlots; i++)
+	{
+		ExecClearTuple(slots[i]);
+		ExecClearTuple(planSlots[i]);
+	}
+	resultRelInfo->ri_NumSlots = 0;
 }
 
 /*
@@ -1263,7 +1270,6 @@ ExecPendingInserts(EState *estate)
 						resultRelInfo->ri_PlanSlots,
 						resultRelInfo->ri_NumSlots,
 						estate, mtstate->canSetTag);
-		resultRelInfo->ri_NumSlots = 0;
 	}
 
 	list_free(estate->es_insert_pending_result_relations);
