From 892a51c3678b9f9bdfa1b52094a68917288dd09f Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Tue, 29 Jul 2003 22:18:38 +0000 Subject: [PATCH] Fix longstanding error in _bt_search(): should moveright at top of loop not bottom. Otherwise we fail to moveright when the root page was split while we were "in flight" to it. This is not a significant problem when the root is above the leaf level, but if the root was also a leaf (ie, a single-page index just got split) we may return the wrong leaf page to the caller, resulting in failure to find a key that is in fact present. Bug has existed at least since 7.1, probably forever. --- src/backend/access/nbtree/nbtsearch.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-) diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c index 56367d2ab3..457914adf7 100644 --- a/src/backend/access/nbtree/nbtsearch.c +++ b/src/backend/access/nbtree/nbtsearch.c @@ -8,7 +8,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.76 2003/07/28 00:09:14 tgl Exp $ + * $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.77 2003/07/29 22:18:38 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -62,6 +62,13 @@ _bt_search(Relation rel, int keysz, ScanKey scankey, BlockNumber par_blkno; BTStack new_stack; + /* + * Race -- the page we just grabbed may have split since we read + * its pointer in the parent (or metapage). If it has, we may need + * to move right to its new sibling. Do that. + */ + *bufP = _bt_moveright(rel, *bufP, keysz, scankey, BT_READ); + /* if this is a leaf page, we're done */ page = BufferGetPage(*bufP); opaque = (BTPageOpaque) PageGetSpecialPointer(page); @@ -99,13 +106,6 @@ _bt_search(Relation rel, int keysz, ScanKey scankey, _bt_relbuf(rel, *bufP); *bufP = _bt_getbuf(rel, blkno, BT_READ); - /* - * Race -- the page we just grabbed may have split since we read - * its pointer in the parent. If it has, we may need to move - * right to its new sibling. Do that. - */ - *bufP = _bt_moveright(rel, *bufP, keysz, scankey, BT_READ); - /* okay, all set to move down a level */ stack_in = new_stack; } @@ -599,8 +599,8 @@ _bt_first(IndexScanDesc scan, ScanDirection dir) /* * At this point we are positioned at the first item >= scan key, or * possibly at the end of a page on which all the existing items are - * greater than the scan key and we know that everything on later - * pages is less than or equal to scan key. + * less than the scan key and we know that everything on later + * pages is greater than or equal to scan key. * * We could step forward in the latter case, but that'd be a waste of * time if we want to scan backwards. So, it's now time to examine