Fix memory in pgoutput for the WAL sender

RelationSyncCache, the hash table in charge of tracking the relation
schemas sent through pgoutput, was forgetting to free the TupleDesc
associated to the two slots used to store the new and old tuples,
causing some memory to be  each time a relation is invalidated
when the slots of an existing relation entry are cleaned up.

This is rather hard to notice as the bloat is pretty minimal, but a
long-running WAL sender would be in trouble over time depending on the
workload.  sysbench has proved to be pretty good at showing the problem,
coupled with some memory monitoring of the WAL sender.

Issue introduced in 52e4f0cd472d, that has added row filters for tables
logically replicated.

Author: Boyu Yang
Reviewed-by: Michael Paquier, Hou Zhijie
Discussion: https://postgr.es/m/DM3PR84MB3442E14B340E553313B5C816E3252@DM3PR84MB3442.NAMPRD84.PROD.OUTLOOK.COM
Back-through: 15

diff --git a/src/backend/replication/pgoutput/pgoutput.c b/src/backend/replication/pgoutput/pgoutput.c
index a6002b223df784a98815c818dc9406f607bdffd8..5e23453f071a99b57e7cc22e16efd91e2e9e7ede 100644 (file)
--- a/src/backend/replication/pgoutput/pgoutput.c
+++ b/src/backend/replication/pgoutput/pgoutput.c
@@ -2095,10 +2095,34 @@ get_rel_sync_entry(PGOutputData *data, Relation relation)
         * Tuple slots cleanups. (Will be rebuilt later if needed).
         */
        if (entry->old_slot)
+       {
+           TupleDesc   desc = entry->old_slot->tts_tupleDescriptor;
+
+           Assert(desc->tdrefcount == -1);
+
            ExecDropSingleTupleTableSlot(entry->old_slot);
+
+           /*
+            * ExecDropSingleTupleTableSlot() would not free the TupleDesc, so
+            * do it now to avoid any s.
+            */
+           FreeTupleDesc(desc);
+       }
        if (entry->new_slot)
+       {
+           TupleDesc   desc = entry->new_slot->tts_tupleDescriptor;
+
+           Assert(desc->tdrefcount == -1);
+
            ExecDropSingleTupleTableSlot(entry->new_slot);
 
+           /*
+            * ExecDropSingleTupleTableSlot() would not free the TupleDesc, so
+            * do it now to avoid any s.
+            */
+           FreeTupleDesc(desc);
+       }
+
        entry->old_slot = NULL;
        entry->new_slot = NULL;