From: Michael Paquier <michael@paquier.xyz>
Date: Tue, 21 Jul 2026 07:50:18 +0000 (+0900)
Subject: Improve generate_partition_qual()'s cache handling on out-of-memory errors
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=fc6425fbe7a1fc7458fc27060ec78c5d98757690;p=thirdparty%2Fpostgresql.git

Improve generate_partition_qual()'s cache handling on out-of-memory errors

An in-flight failure when trying to set rd_partcheckcxt or
rd_partcheck, while for example doing an allocation in copyObject(),
would leave a backend cache in a corrupted state.  The operations are
now ordered so as we avoid a leak in the cache memory context and a
semi-filled cache state when an allocation failure happens.

This is unlikely going to be hit in practice.  Like the other
improvements of this kind, no backpatch is done.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Author: Matthias van de Meent <boekewurm+postgres@gmail.com>
Discussion: https://postgr.es/m/95c64dc2-3abe-4f4e-b285-4c681f565d9f@gmail.com
---

diff --git a/src/backend/utils/cache/partcache.c b/src/backend/utils/cache/partcache.c
index 3107075c9ad..a0982674884 100644
--- a/src/backend/utils/cache/partcache.c
+++ b/src/backend/utils/cache/partcache.c
@@ -411,14 +411,31 @@ generate_partition_qual(Relation rel)
 	 */
 	if (result != NIL)
 	{
-		rel->rd_partcheckcxt = AllocSetContextCreate(CacheMemoryContext,
-													 "partition constraint",
-													 ALLOCSET_SMALL_SIZES);
-		MemoryContextCopyAndSetIdentifier(rel->rd_partcheckcxt,
+		/*
+		 * Take care to order operations so that allocation errors don't leave
+		 * the catcache in an invalid state; first allocate everything into a
+		 * transactional context, then associate it with CacheContext and
+		 * update the relation data.  This also avoids leaking memory if we
+		 * ever hit OOM here.
+		 */
+		List	   *partcheck;
+		MemoryContext partctx;
+
+		partctx = AllocSetContextCreate(CurrentMemoryContext,
+										"partition constraint",
+										ALLOCSET_SMALL_SIZES);
+		MemoryContextCopyAndSetIdentifier(partctx,
 										  RelationGetRelationName(rel));
-		oldcxt = MemoryContextSwitchTo(rel->rd_partcheckcxt);
-		rel->rd_partcheck = copyObject(result);
+
+		oldcxt = MemoryContextSwitchTo(partctx);
+		partcheck = copyObject(result);
 		MemoryContextSwitchTo(oldcxt);
+
+		/* finally, link the allocations and memctx into the right places */
+		MemoryContextSetParent(partctx, CacheMemoryContext);
+
+		rel->rd_partcheckcxt = partctx;
+		rel->rd_partcheck = partcheck;
 	}
 	else
 		rel->rd_partcheck = NIL;