From fa2629b7eaa46d1295843f091c45e107b19cadd7 Mon Sep 17 00:00:00 2001
From: "Vadim B. Mikheev" <vadim4o@yahoo.com>
Date: Wed, 9 Apr 1997 01:52:04 +0000
Subject: [PATCH] Fix (hack) IndexSelectivity(): use sum(npages)/((nkeys == 1)
? 1 : nkeys + 1) as expected index page estimation for multi-key quals -
instead of sum(npages). In old code npages for x > 10 and x < 20 is twice as
for x > 10 - cool ?
---
src/backend/optimizer/util/plancat.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index 7a108578ed1..eda5830d2cf 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/optimizer/util/plancat.c,v 1.4 1997/03/12 21:06:14 scrappy Exp $
+ * $Header: /cvsroot/pgsql/src/backend/optimizer/util/plancat.c,v 1.5 1997/04/09 01:52:04 vadim Exp $
*
*-------------------------------------------------------------------------
*/
@@ -564,9 +564,17 @@ IndexSelectivity(Oid indexrelid,
(char *) constFlags[n],
(char *) nIndexKeys,
(char *) indexrelid);
+#if 0
+/*
+ * So cool guys! Npages for x > 10 and x < 20 is twice as
+ * npages for x > 10! - vadim 04/09/97
+ */
npages += PointerIsValid(amopnpages) ? *amopnpages : 0.0;
if ((i = npages) < npages) /* ceil(npages)? */
npages += 1.0;
+#endif
+ npages += PointerIsValid(amopnpages) ? *amopnpages : 0.0;
+
amopselect = (float64) fmgr(amop->amopselect,
(char *) operatorObjectIds[n],
(char *) indrelid,
@@ -577,7 +585,13 @@ IndexSelectivity(Oid indexrelid,
(char *) indexrelid);
select *= PointerIsValid(amopselect) ? *amopselect : 1.0;
}
- *idxPages = npages;
+ /*
+ * Estimation of npages below is hack of course, but it's
+ * better than it was before. - vadim 04/09/97
+ */
+ if ( nIndexKeys > 1 )
+ npages = npages / (1.0 + nIndexKeys);
+ *idxPages = ceil ((double)(npages/nIndexKeys));
*idxSelec = select;
}
--
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