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I've attached a patch which implements Bob Jenkin's hash function for

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PostgreSQL. This hash function replaces the one used by hash indexes and
the catalog cache. Hash joins use a different, relatively poor-quality
hash function, but I'll fix that later.

As suggested by Tom Lane, this patch also changes the size of the fixed
hash table used by the catalog cache to be a power-of-2 (instead of a
prime: I chose 256 instead of 257). This allows the catcache to lookup
hash buckets using a simple bitmask. This should improve the performance
of the catalog cache slightly, since the previous method (modulo a
prime) was slow.

In my tests, this improves the performance of hash indexes by between 4%
and 8%; the performance when using btree indexes or seqscans is
basically unchanged.

Neil Conway <neilconway@rogers.com>
This commit is contained in:
Bruce Momjian
2002-03-06 20:49:46 +00:00
parent 5b5cef9abd
commit 7ab7467318
10 changed files with 124 additions and 94 deletions
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10
src/include/access/hash.h
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Id: hash.h,v 1.43 2002/02/25 04:06:52 momjian Exp $
* $Id: hash.h,v 1.44 2002/03/06 20:49:45 momjian Exp $
*
* NOTES
* modeled after Margo Seltzer's hash implementation for unix.
@@ -265,8 +265,7 @@ extern Datum hashoidvector(PG_FUNCTION_ARGS);
extern Datum hashint2vector(PG_FUNCTION_ARGS);
extern Datum hashname(PG_FUNCTION_ARGS);
extern Datum hashvarlena(PG_FUNCTION_ARGS);
extern Datum hash_any(const char *keydata, int keylen);
extern Datum hash_any(register const char *k, register int keylen);
/* private routines */
@@ -288,7 +287,7 @@ extern void _hash_metapinit(Relation rel);
extern Buffer _hash_getbuf(Relation rel, BlockNumber blkno, int access);
extern void _hash_relbuf(Relation rel, Buffer buf, int access);
extern void _hash_wrtbuf(Relation rel, Buffer buf);
extern void _hash_wrtnorelbuf(Relation rel, Buffer buf);
extern void _hash_wrtnorelbuf(Buffer buf);
extern Page _hash_chgbufaccess(Relation rel, Buffer *bufp, int from_access,
int to_access);
extern void _hash_pageinit(Page page, Size size);
@@ -313,8 +312,7 @@ extern bool _hash_step(IndexScanDesc scan, Buffer *bufP, ScanDirection dir,
/* hashutil.c */
extern ScanKey _hash_mkscankey(Relation rel, IndexTuple itup,
HashMetaPage metap);
extern ScanKey _hash_mkscankey(Relation rel, IndexTuple itup);
extern void _hash_freeskey(ScanKey skey);
extern bool _hash_checkqual(IndexScanDesc scan, IndexTuple itup);
extern HashItem _hash_formitem(IndexTuple itup);