The main speed improvement is for varchar datatype. I think It should be
mention here as well. IIRC, times are similar with B-Tree for integer
datatype.
Zdenek
Kenneth Marshall píše v st 04. 02. 2009 v 13:57 -0600:
> 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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>