From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Yangyang <yangyangbm(at)gmail(dot)com> |
Cc: | pgsql-novice(at)postgresql(dot)org |
Subject: | Re: How can I make PostgreSQL to select another quey plan? |
Date: | 2011-11-30 16:11:26 |
Message-ID: | 12498.1322669486@sss.pgh.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-novice |
Yangyang <yangyangbm(at)gmail(dot)com> writes:
> I'm trying to force the database to select another query plan for a
> query, rather than the optimal one.
> I changed query tuning related parameters, but the query plan stays
> the same. Although the costs for nodes changed correspondingly,
> What parameters can I modify to force the DB to select another plan?
There are the enable_xxx flags, or if the problem is a bad join order
you could reduce the join_collapse_limit setting to 1 and use JOIN
syntax to specify the join order. If you'd like it to not use a
particular index you could transiently drop that index:
begin;
drop index ...;
explain ...;
rollback;
I recently rewrote the manual's discussion of using explain, so
you might care to read this:
http://developer.postgresql.org/pgdocs/postgres/using-explain.html
although it does refer to a couple of features that don't exist in
production releases yet.
regards, tom lane
From | Date | Subject | |
---|---|---|---|
Next Message | Yangyang | 2011-11-30 16:18:45 | Re: How can I make PostgreSQL to select another quey plan? |
Previous Message | Yangyang | 2011-11-30 16:07:14 | Re: How can I make PostgreSQL to select another quey plan? |