Fix "failed to re-find parent key" btree VACUUM failure by tweaking

_bt_pagedel to recover from the failure: just search the whole parent level
if searching to the right fails.  This does nothing for the underlying problem
that index keys became out-of-order in the grandparent level.  However, we
believe that there is no other consequence worse than slightly inefficient
searching, so this narrow patch seems like the safest solution for the back
branches.

1 files changed, 18 insertions, 6 deletions

diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c
index 378c5f9d36f..03b8ca3b4ab 100644
--- a/src/backend/access/nbtree/nbtpage.c
+++ b/src/backend/access/nbtree/nbtpage.c
@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtpage.c,v 1.81.4.1 2005/05/07 21:32:53 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/nbtree/nbtpage.c,v 1.81.4.2 2006/11/01 19:50:08 tgl Exp $
  *
  *	NOTES
  *	   Postgres btree pages look like ordinary relation pages.	The opaque
@@ -867,16 +867,28 @@ _bt_pagedel(Relation rel, Buffer buf, bool vacuum_full)
 	rbuf = _bt_getbuf(rel, rightsib, BT_WRITE);
 
 	/*
-	 * Next find and write-lock the current parent of the target page.
-	 * This is essentially the same as the corresponding step of
-	 * splitting.
+	 * Next find and write-lock the current parent of the target page. This is
+	 * essentially the same as the corresponding step of splitting.  However,
+	 * it's possible for the search to fail (for reasons explained in README).
+	 * If that happens, we recover by searching the whole parent level, which
+	 * is a tad inefficient but doesn't happen often enough to be a problem.
 	 */
 	ItemPointerSet(&(stack->bts_btitem.bti_itup.t_tid),
 				   target, P_HIKEY);
 	pbuf = _bt_getstackbuf(rel, stack, BT_WRITE);
 	if (pbuf == InvalidBuffer)
-		elog(ERROR, "failed to re-find parent key in \"%s\"",
-			 RelationGetRelationName(rel));
+	{
+		/* Find the leftmost page in the parent level */
+		pbuf = _bt_get_endpoint(rel, opaque->btpo.level + 1, false);
+		stack->bts_blkno = BufferGetBlockNumber(pbuf);
+		stack->bts_offset = InvalidOffsetNumber;
+		_bt_relbuf(rel, pbuf);
+		/* and repeat search from there */
+		pbuf = _bt_getstackbuf(rel, stack, BT_WRITE);
+		if (pbuf == InvalidBuffer)
+			elog(ERROR, "failed to re-find parent key in \"%s\" for deletion target page %u",
+				 RelationGetRelationName(rel), target);
+	}
 	parent = stack->bts_blkno;
 	poffset = stack->bts_offset;