1 files changed, 46 insertions, 17 deletions

diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index 4d0254f8e07..8fb7a750d74 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -3166,39 +3166,68 @@ RelationSetNewRelfilenode(Relation relation, char persistence,
 	RelationDropStorage(relation);
 
 	/*
-	 * Now update the pg_class row.  However, if we're dealing with a mapped
-	 * index, pg_class.relfilenode doesn't change; instead we have to send the
-	 * update to the relation mapper.
+	 * If we're dealing with a mapped index, pg_class.relfilenode doesn't
+	 * change; instead we have to send the update to the relation mapper.
+	 *
+	 * For mapped indexes, we don't actually change the pg_class entry at all;
+	 * this is essential when reindexing pg_class itself.  That leaves us with
+	 * possibly-inaccurate values of relpages etc, but those will be fixed up
+	 * later.
 	 */
 	if (RelationIsMapped(relation))
+	{
+		/* This case is only supported for indexes */
+		Assert(relation->rd_rel->relkind == RELKIND_INDEX);
+
+		/* Since we're not updating pg_class, these had better not change */
+		Assert(classform->relfrozenxid == freezeXid);
+		Assert(classform->relminmxid == minmulti);
+		Assert(classform->relpersistence == persistence);
+
+		/*
+		 * In some code paths it's possible that the tuple update we'd
+		 * otherwise do here is the only thing that would assign an XID for
+		 * the current transaction.  However, we must have an XID to delete
+		 * files, so make sure one is assigned.
+		 */
+		(void) GetCurrentTransactionId();
+
+		/* Do the deed */
 		RelationMapUpdateMap(RelationGetRelid(relation),
 							 newrelfilenode,
 							 relation->rd_rel->relisshared,
 							 false);
+
+		/* Since we're not updating pg_class, must trigger inval manually */
+		CacheInvalidateRelcache(relation);
+	}
 	else
+	{
+		/* Normal case, update the pg_class entry */
 		classform->relfilenode = newrelfilenode;
 
-	/* These changes are safe even for a mapped relation */
-	if (relation->rd_rel->relkind != RELKIND_SEQUENCE)
-	{
-		classform->relpages = 0;	/* it's empty until further notice */
-		classform->reltuples = 0;
-		classform->relallvisible = 0;
-	}
-	classform->relfrozenxid = freezeXid;
-	classform->relminmxid = minmulti;
-	classform->relpersistence = persistence;
+		/* relpages etc. never change for sequences */
+		if (relation->rd_rel->relkind != RELKIND_SEQUENCE)
+		{
+			classform->relpages = 0;	/* it's empty until further notice */
+			classform->reltuples = 0;
+			classform->relallvisible = 0;
+		}
+		classform->relfrozenxid = freezeXid;
+		classform->relminmxid = minmulti;
+		classform->relpersistence = persistence;
 
-	simple_heap_update(pg_class, &tuple->t_self, tuple);
-	CatalogUpdateIndexes(pg_class, tuple);
+		simple_heap_update(pg_class, &tuple->t_self, tuple);
+		CatalogUpdateIndexes(pg_class, tuple);
+	}
 
 	heap_freetuple(tuple);
 
 	heap_close(pg_class, RowExclusiveLock);
 
 	/*
-	 * Make the pg_class row change visible, as well as the relation map
-	 * change if any.  This will cause the relcache entry to get updated, too.
+	 * Make the pg_class row change or relation map change visible.  This will
+	 * cause the relcache entry to get updated, too.
 	 */
 	CommandCounterIncrement();