Fix stale values in partition map entries on subscribers.

Amit Kapila · Amit Kapila · commit 419c72715172 · 2022-06-21T15:12:52.000+05:30
We build the partition map entries on subscribers while applying the changes for update/delete on partitions. The component relation in each entry is closed after its use so we need to update it on successive use of cache entries. This problem was there since the original commit f1ac27b that introduced this code but we didn't notice it till the recent commit 26b3455 started to use the component relation of partition map cache entry. Reported-by: Tom Lane, as per buildfarm Author: Amit Langote, Hou Zhijie Reviewed-by: Amit Kapila, Shi Yu Backpatch-through: 13, where it was introduced Discussion: https://postgr.es/m/OSZPR01MB6310F46CD425A967E4AEF736FDA49@OSZPR01MB6310.jpnprd01.prod.outlook.com
diff --git a/src/backend/replication/logical/relation.c b/src/backend/replication/logical/relation.c
@@ -564,8 +564,20 @@ logicalrep_partition_open(LogicalRepRelMapEntry *root,
 
 	entry = &part_entry->relmapentry;
 
+	/*
+	 * We must always overwrite entry->localrel with the latest partition
+	 * Relation pointer, because the Relation pointed to by the old value may
+	 * have been cleared after the caller would have closed the partition
+	 * relation after the last use of this entry.  Note that localrelvalid is
+	 * only updated by the relcache invalidation callback, so it may still be
+	 * true irrespective of whether the Relation pointed to by localrel has
+	 * been cleared or not.
+	 */
 	if (found && entry->localrelvalid)
+	{
+		entry->localrel = partrel;
 		return entry;
+	}
 
 	/* Switch to longer-lived context. */
 	oldctx = MemoryContextSwitchTo(LogicalRepPartMapContext);
