Re: <note> on hash indexes

From: Kenneth Marshall <ktm(at)rice(dot)edu>
To: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Cc: Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: <note> on hash indexes
Date: 2009-02-04 19:57:57
Message-ID: 20090204195756.GA2995@it.is.rice.edu
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I had submitted the documentation change as part of my
hash function patch but it was removed as not relevant.
(It wasn't really.) I would basically remove the first
sentence:

Note: Hash index operations are not presently WAL-logged,
so hash indexes might need to be rebuilt with REINDEX after a
database crash. For this reason, hash index use is presently
discouraged.

Ken

On Wed, Feb 04, 2009 at 01:22:23PM -0300, Alvaro Herrera wrote:
> Hi,
>
> indices.sgml contains this paragraph about hash indexes:
>
> Note: Testing has shown PostgreSQL's hash indexes to perform no
> better than B-tree indexes, and the index size and build time for hash
> indexes is much worse. Furthermore, hash index operations are not
> presently WAL-logged, so hash indexes might need to be rebuilt with
> REINDEX after a database crash. For these reasons, hash index use is
> presently discouraged.
>
>
> However, it seems to me that hash indexes are much improved in 8.4, so
> maybe this needs to be reworded. I'm not sure to what point they have
> been improved though.
>
> --
> Alvaro Herrera http://www.CommandPrompt.com/
> PostgreSQL Replication, Consulting, Custom Development, 24x7 support
>
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