From 5ac2d7c0ebdb1071643f77a6f1fa1a54fd469fb8 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 2 Sep 2003 22:10:16 +0000
Subject: [PATCH] In _bt_check_unique() loop, don't bother applying
_bt_isequal() to killed items; just skip to the next item immediately. Only
check for key equality when we reach a non-killed item or the end of the
index page. This saves key comparisons when there are lots of killed items,
as for example in a heavily-updated table that's not been vacuumed lately.
Seems to be a win for pgbench anyway.
---
src/backend/access/nbtree/nbtinsert.c | 42 +++++++++++++++++----------
1 file changed, 27 insertions(+), 15 deletions(-)
diff --git a/src/backend/access/nbtree/nbtinsert.c b/src/backend/access/nbtree/nbtinsert.c
index 02d842434c2..c8dbbfb0415 100644
--- a/src/backend/access/nbtree/nbtinsert.c
+++ b/src/backend/access/nbtree/nbtinsert.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.104 2003/08/04 02:39:57 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtinsert.c,v 1.105 2003/09/02 22:10:16 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -189,27 +189,39 @@ _bt_check_unique(Relation rel, BTItem btitem, Relation heapRel,
BlockNumber nblkno;
/*
- * make sure the offset points to an actual key before trying to
- * compare it...
+ * make sure the offset points to an actual item before trying to
+ * examine it...
*/
if (offset <= maxoff)
{
- /*
- * _bt_compare returns 0 for (1,NULL) and (1,NULL) - this's
- * how we handling NULLs - and so we must not use _bt_compare
- * in real comparison, but only for ordering/finding items on
- * pages. - vadim 03/24/97
- */
- if (!_bt_isequal(itupdesc, page, offset, natts, itup_scankey))
- break; /* we're past all the equal tuples */
-
curitemid = PageGetItemId(page, offset);
/*
- * We can skip the heap fetch if the item is marked killed.
+ * We can skip items that are marked killed.
+ *
+ * Formerly, we applied _bt_isequal() before checking the kill
+ * flag, so as to fall out of the item loop as soon as possible.
+ * However, in the presence of heavy update activity an index
+ * may contain many killed items with the same key; running
+ * _bt_isequal() on each killed item gets expensive. Furthermore
+ * it is likely that the non-killed version of each key appears
+ * first, so that we didn't actually get to exit any sooner anyway.
+ * So now we just advance over killed items as quickly as we can.
+ * We only apply _bt_isequal() when we get to a non-killed item or
+ * the end of the page.
*/
if (!ItemIdDeleted(curitemid))
{
+ /*
+ * _bt_compare returns 0 for (1,NULL) and (1,NULL) - this's
+ * how we handling NULLs - and so we must not use _bt_compare
+ * in real comparison, but only for ordering/finding items on
+ * pages. - vadim 03/24/97
+ */
+ if (!_bt_isequal(itupdesc, page, offset, natts, itup_scankey))
+ break; /* we're past all the equal tuples */
+
+ /* okay, we gotta fetch the heap tuple ... */
cbti = (BTItem) PageGetItem(page, curitemid);
htup.t_self = cbti->bti_itup.t_tid;
if (heap_fetch(heapRel, SnapshotDirty, &htup, &hbuffer,
@@ -1547,7 +1559,7 @@ _bt_pgaddtup(Relation rel,
* _bt_isequal - used in _bt_doinsert in check for duplicates.
*
* This is very similar to _bt_compare, except for NULL handling.
- * Rule is simple: NOT_NULL not equal NULL, NULL not_equal NULL too.
+ * Rule is simple: NOT_NULL not equal NULL, NULL not equal NULL too.
*/
static bool
_bt_isequal(TupleDesc itupdesc, Page page, OffsetNumber offnum,
@@ -1576,7 +1588,7 @@ _bt_isequal(TupleDesc itupdesc, Page page, OffsetNumber offnum,
datum = index_getattr(itup, attno, itupdesc, &isNull);
/* NULLs are never equal to anything */
- if (entry->sk_flags & SK_ISNULL || isNull)
+ if ((entry->sk_flags & SK_ISNULL) || isNull)
return false;
result = DatumGetInt32(FunctionCall2(&entry->sk_func,
--
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