Code review for recent changes in relcache.c.

tglsfdc · tglsfdc · commit e7a9020939c9 · 2014-05-14T14:55:50.000-04:00
rd_replidindex should be managed the same as rd_oidindex, and rd_keyattr
and rd_idattr should be managed like rd_indexattr.  Omissions in this area
meant that the bitmapsets computed for rd_keyattr and rd_idattr would be
leaked during any relcache flush, resulting in a slow but permanent leak in
CacheMemoryContext.  There was also a tiny probability of relcache entry
corruption if we ran out of memory at just the wrong point in
RelationGetIndexAttrBitmap.  Otherwise, the fields were not zeroed where
expected, which would not bother the code any AFAICS but could greatly
confuse anyone examining the relcache entry while debugging.

Also, create an API function RelationGetReplicaIndex rather than letting
non-relcache code be intimate with the mechanisms underlying caching of
that value (we won't even mention the memory leak there).

Also, fix a relcache flush hazard identified by Andres Freund:
RelationGetIndexAttrBitmap must not assume that rd_replidindex stays valid
across index_open.

The aspects of this involving rd_keyattr date back to 9.3, so back-patch
those changes.
diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
@@ -1829,6 +1829,7 @@ RelationDestroyRelation(Relation relation)
 		FreeTupleDesc(relation->rd_att);
 	list_free(relation->rd_indexlist);
 	bms_free(relation->rd_indexattr);
+	bms_free(relation->rd_keyattr);
 	FreeTriggerDesc(relation->trigdesc);
 	if (relation->rd_options)
 		pfree(relation->rd_options);
@@ -3594,7 +3595,8 @@ insert_ordered_oid(List *list, Oid datum)
  * 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.
+ * wrong rd_indexattr set to get computed and cached.  Likewise, we do not
+ * touch rd_keyattr.
  */
 void
 RelationSetIndexList(Relation relation, List *indexIds, Oid oidIndex)
@@ -3875,10 +3877,16 @@ RelationGetIndexAttrBitmap(Relation relation, bool keyAttrs)
 
 	list_free(indexoidlist);
 
-	/* Now save a copy of the bitmap in the relcache entry. */
+	/*
+	 * Now save copies of the bitmaps in the relcache entry.  We intentionally
+	 * set rd_indexattr last, because that's the one that signals validity of
+	 * the values; if we run out of memory before making that copy, we won't
+	 * leave the relcache entry looking like the other ones are valid but
+	 * empty.
+	 */
 	oldcxt = MemoryContextSwitchTo(CacheMemoryContext);
-	relation->rd_indexattr = bms_copy(indexattrs);
 	relation->rd_keyattr = bms_copy(uindexattrs);
+	relation->rd_indexattr = bms_copy(indexattrs);
 	MemoryContextSwitchTo(oldcxt);
 
 	/* We return our original working copy for caller to play with */
@@ -4423,6 +4431,7 @@ load_relcache_init_file(bool shared)
 		rel->rd_indexvalid = 0;
 		rel->rd_indexlist = NIL;
 		rel->rd_indexattr = NULL;
+		rel->rd_keyattr = NULL;
 		rel->rd_oidindex = InvalidOid;
 		rel->rd_createSubid = InvalidSubTransactionId;
 		rel->rd_newRelfilenodeSubid = InvalidSubTransactionId;
