| From: | Neil Conway <neilc(at)samurai(dot)com> |
|---|---|
| To: | Luke Lonergan <llonergan(at)greenplum(dot)com> |
| Cc: | "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Skype Technologies OY <hannu(at)skype(dot)net>, mark(at)mark(dot)mielke(dot)cc, Bruce Momjian <bruce(at)momjian(dot)us>, Jie Zhang <jzhang(at)greenplum(dot)com>, Gavin Sherry <swm(at)linuxworld(dot)com(dot)au>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Hash indexes (was: On-disk bitmap index patch) |
| Date: | 2006-08-01 16:03:21 |
| Message-ID: | 1154448201.17804.5.camel@localhost |
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| Lists: | pgsql-hackers |
On Tue, 2006-08-01 at 07:55 -0700, Luke Lonergan wrote:
> WRT hashing - we use FNV hash which is a very nice, very fast modern hash
> algorithm. We would contribute that if we worked on this.
We currently use Bob Jenkins' hash function[1], which is apparently
faster than FNV on most architectures except the Pentium IV (because the
P4 has slow shifting -- see [2]). I haven't compared their collision
rates -- it may be that we could improve matters incrementally by
switching to FNV, but the fundamental problems with our hash index
implementation lie elsewhere.
-Neil
[1] http://burtleburtle.net/bob/hash/doobs.html
[2] http://www.azillionmonkeys.com/qed/hash.html
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