Fix corner-case bug introduced with HOT: if REINDEX TABLE pg_class (or a

REINDEX DATABASE including same) is done before a session has done any other
update on pg_class, the pg_class relcache entry was left with an incorrect
setting of rd_indexattr, because the indexed-attributes set would be first
demanded at a time when we'd forced a partial list of indexes into the
pg_class entry, and it would remain cached after that.  This could result
in incorrect decisions about HOT-update safety later in the same session.
In practice, since only pg_class_relname_nsp_index would be missed out,
only ALTER TABLE RENAME and ALTER TABLE SET SCHEMA could trigger a problem.
Per report and test case from Ondrej Jirman.

src/backend/catalog/index.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/catalog/index.c,v 1.300 2008/06/19 00:46:04 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/catalog/index.c,v 1.301 2008/08/10 19:02:33 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -2380,9 +2380,13 @@ reindex_relation(Oid relid, bool toast_too)
 	 * problem.
 	 */
 	is_pg_class = (RelationGetRelid(rel) == RelationRelationId);
-	doneIndexes = NIL;
+
+	/* Ensure rd_indexattr is valid; see comments for RelationSetIndexList */
+	if (is_pg_class)
+		(void) RelationGetIndexAttrBitmap(rel);
 
 	/* Reindex all the indexes. */
+	doneIndexes = NIL;
 	foreach(indexId, indexIds)
 	{
 		Oid			indexOid = lfirst_oid(indexId);

src/backend/utils/cache/relcache.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/cache/relcache.c,v 1.272 2008/05/12 00:00:52 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/cache/relcache.c,v 1.273 2008/08/10 19:02:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2986,6 +2986,13 @@ insert_ordered_oid(List *list, Oid datum)
  * messages.  In practice it is only used on pg_class (see REINDEX).
  *
  * It is up to the caller to make sure the given list is correctly ordered.
+ *
+ * We deliberately do not change rd_indexattr here: even when operating
+ * with a temporary partial index list, HOT-update decisions must be made
+ * correctly with respect to the full index set.  It is up to the caller
+ * to ensure that a correct rd_indexattr set has been cached before first
+ * calling RelationSetIndexList; else a subsequent inquiry might cause a
+ * wrong rd_indexattr set to get computed and cached.
  */
 void
 RelationSetIndexList(Relation relation, List *indexIds, Oid oidIndex)
@@ -3004,7 +3011,6 @@ RelationSetIndexList(Relation relation, List *indexIds, Oid oidIndex)
 	relation->rd_indexvalid = 2;	/* mark list as forced */
 	/* must flag that we have a forced index list */
 	need_eoxact_work = true;
-	/* we deliberately do not change rd_indexattr */
 }
 
 /*