From here:
http://osdb.sourceforge.net/
We find this quote:
"For you long-suffering OSDB PostgreSQL users, we offer 

--postgresql=no_hash_index 

to work around the hash index problems of OSDB with PostgreSQL V7.1 and
7.2. As always, let us know of any problems. May the source be with
you!"

Does anyone know what the above is all about?

Mon, 22 Apr 2002 14:15:37 -0700
"Dann Corbit" <DCorbit@connx.com>
What is wrong with hashed index usage?
On Mon, 22 Apr 2002 14:15:37 -0700
"Dann Corbit" <DCorbit@connx.com> wrote:
> From here:
> http://osdb.sourceforge.net/
> We find this quote:
> "For you long-suffering OSDB PostgreSQL users, we offer 
> 
> --postgresql=no_hash_index 
> 
> to work around the hash index problems of OSDB with PostgreSQL V7.1 and
> 7.2. As always, let us know of any problems. May the source be with
> you!"
> 
> Does anyone know what the above is all about?

Yes -- search the list archives, or check the PostgreSQL docs. This problem
has been brought up several times: hash indexes deadlock under concurrent
load. A run of pgbench with a reasonably high concurrency level (10 or 15)
produces the problem consistently.

Previously, I had volunteered to fix this, but

    (a) I'm busy with the PREPARE/EXECUTE stuff at the moment.

    (b) I'm not sure it's worth the investment of time: AFAIK,
        hash indexes don't have many advantages over btrees for
        scalar data.

On the other hand, if someone steps forward with some data on a
specific advantage that hash indexes have over btrees, I don't
expect that the concurrency problems should be too difficult to
solve.

Cheers,

Neil

-- 
Neil Conway <neilconway@rogers.com>
PGP Key ID: DB3C29FC

Mon, 22 Apr 2002 17:59:16 -0400
Neil Conway <nconway@klamath.dyndns.org>
Re: What is wrong with hashed index usage?