From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
---|---|
To: | Antonio Carlos Salzvedel Furtado Junior <acsfj08(at)inf(dot)ufpr(dot)br> |
Cc: | pgsql-novice(at)postgresql(dot)org |
Subject: | Re: Changing tuning parameters with EXPLAIN |
Date: | 2012-06-04 21:01:08 |
Message-ID: | 1338843668.27297.2.camel@sussancws0025 |
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Lists: | pgsql-novice |
On Mon, 2012-06-04 at 17:49 -0300, Antonio Carlos Salzvedel Furtado
Junior wrote:
> Hello PostgreSQL users,
>
> I've been working with the estimated cost from EXPLAIN. I was
> wondering if I could change the tuning parameters, to produce new
> estimated costs, without interfering with the database workload. Is it
> possible?
>
> I'm changing these parameters by executing SQL queries ("SET"). The
> problem is that once I change these parameters, the query optimizer
> will start using these values to build their query plans.
If you issue a SET, it only affects queries executed in your connection
(the session). So this is safe for EXPLAINing queries. If you do a "SET
LOCAL" within a transaction, it will only affect that transaction.
To make the values persist and get picked up by other connections, you
need to set them in postgresql.conf and send a SIGHUP (or restart, of
course).
Regards,
Jeff Davis
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