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Commit892a51c

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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 whilewe were "in flight" to it. This is not a significant problem when the rootis above the leaf level, but if the root was also a leaf (ie, a single-pageindex 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 existedat least since 7.1, probably forever.
1 parent5e3c09a commit892a51c

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‎src/backend/access/nbtree/nbtsearch.c

Lines changed: 10 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* IDENTIFICATION
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* $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.76 2003/07/28 00:09:14 tgl Exp $
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* $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtsearch.c,v 1.77 2003/07/29 22:18:38 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -62,6 +62,13 @@ _bt_search(Relation rel, int keysz, ScanKey scankey,
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BlockNumberpar_blkno;
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BTStacknew_stack;
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/*
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* Race -- the page we just grabbed may have split since we read
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* its pointer in the parent (or metapage). If it has, we may need
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* to move right to its new sibling. Do that.
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*/
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*bufP=_bt_moveright(rel,*bufP,keysz,scankey,BT_READ);
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/* if this is a leaf page, we're done */
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page=BufferGetPage(*bufP);
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opaque= (BTPageOpaque)PageGetSpecialPointer(page);
@@ -99,13 +106,6 @@ _bt_search(Relation rel, int keysz, ScanKey scankey,
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_bt_relbuf(rel,*bufP);
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*bufP=_bt_getbuf(rel,blkno,BT_READ);
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/*
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* Race -- the page we just grabbed may have split since we read
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* its pointer in the parent. If it has, we may need to move
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* right to its new sibling. Do that.
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*/
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*bufP=_bt_moveright(rel,*bufP,keysz,scankey,BT_READ);
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/* okay, all set to move down a level */
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stack_in=new_stack;
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}
@@ -599,8 +599,8 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
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/*
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* At this point we are positioned at the first item >= scan key, or
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* possibly at the end of a page on which all the existing items are
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*greater than the scan key and we know that everything on later
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* pages isless than or equal to scan key.
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*less than the scan key and we know that everything on later
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* pages isgreater than or equal to scan key.
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*
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* We could step forward in the latter case, but that'd be a waste of
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* time if we want to scan backwards. So, it's now time to examine

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