Fix memory leak in pgoutput with relation attribute map

pgoutput caches the attribute map of a relation, that is free()'d only
when validating a RelationSyncEntry.  However, this code path is not
taken when calling any of the SQL functions able to do some logical
decoding, like pg_logical_slot_{get,peek}_changes(), leaking some memory
into CacheMemoryContext on repeated calls.

To address this, a relation's attribute map is allocated in
PGOutputData's cachectx, free()'d at the end of the execution of these
SQL functions when logical decoding ends.  This is available down to 15.
v13 and v14 have a similar leak, which will be dealt with later.

Reported-by: Masahiko Sawada
Author: Vignesh C
Reviewed-by: Hou Zhijie
Discussion: https://postgr.es/m/CAD21AoDkAhQVSukOfH3_reuF-j4EU0-HxMqU3dU+bSTxsqT14Q@mail.gmail.com
Discussion: https://postgr.es/m/CALDaNm1hewNAsZ_e6FF52a=9drmkRJxtEPrzCB6-9mkJyeBBqA@mail.gmail.com
Backpatch-through: 15

diff --git a/src/backend/replication/pgoutput/pgoutput.c b/src/backend/replication/pgoutput/pgoutput.c
index 807ba8c3d64ddc00f95201de71f33fbdb4b58a33..99518c6b6dd1e8ed8e5325cfb37d426f4d4084ae 100644 (file)
--- a/src/backend/replication/pgoutput/pgoutput.c
+++ b/src/backend/replication/pgoutput/pgoutput.c
@@ -1184,8 +1184,8 @@ init_tuple_slot(PGOutputData *data, Relation relation,
                TupleDesc       indesc = RelationGetDescr(relation);
                TupleDesc       outdesc = RelationGetDescr(ancestor);
 
-               /* Map must live as long as the session does. */
-               oldctx = MemoryContextSwitchTo(CacheMemoryContext);
+               /* Map must live as long as the logical decoding context. */
+               oldctx = MemoryContextSwitchTo(data->cachectx);
 
                entry->attrmap = build_attrmap_by_name_if_req(indesc, outdesc, false);