Re: on hash indexes - Mailing list pgsql-hackers

From Kenneth Marshall
Subject Re: on hash indexes
Date
Msg-id 20090204195756.GA2995@it.is.rice.edu
Whole thread Raw
In response to on hash indexes  (Alvaro Herrera <alvherre@commandprompt.com>)
Responses Re: on hash indexes  (Zdenek Kotala <Zdenek.Kotala@Sun.COM>)
Re: on hash indexes  (Bruce Momjian <bruce@momjian.us>)
List pgsql-hackers
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
aftera 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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