From: Simon Riggs <simon@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jean-Philippe Côté <jean-philippe.cote@crt.umontreal.ca>
Cc: pgsql-performance@postgresql.org
Subject: Re: Extremely irregular query performance
Date: Thu, 12 Jan 2006 09:48:41 +0000
Message-ID: <1137059321.3180.34.camel@localhost.localdomain> (raw)
In-Reply-To: <480.1137036235@sss.pgh.pa.us>
References: <20060111234149.05DEA384099@crt0.crt.umontreal.ca>
<480.1137036235@sss.pgh.pa.us>
On Wed, 2006-01-11 at 22:23 -0500, Tom Lane wrote:
> =?iso-8859-1?Q?Jean-Philippe_C=F4t=E9?= <jean-philippe.cote@crt.umontreal.ca> writes:
> > Thanks a lot for this info, I was indeed exceeding the genetic
> > optimizer's threshold. Now that it is turned off, I get
> > a very stable response time of 435ms (more or less 5ms) for
> > the same query. It is about three times slower than the best
> > I got with the genetic optimizer on, but the overall average
> > is much lower.
>
> Hmm. It would be interesting to use EXPLAIN ANALYZE to confirm that the
> plan found this way is the same as the best plan found by GEQO, and
> the extra couple hundred msec is the price you pay for the exhaustive
> plan search. If GEQO is managing to find a plan better than the regular
> planner then we need to look into why ...
It seems worth noting in the EXPLAIN whether GEQO has been used to find
the plan, possibly along with other factors influencing the plan such as
enable_* settings.
Best Regards, Simon Riggs
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To: pgsql-performance@postgresql.org
Cc: simon@2ndquadrant.com, tgl@sss.pgh.pa.us, jean-philippe.cote@crt.umontreal.ca
Subject: Re: Extremely irregular query performance
In-Reply-To: <1137059321.3180.34.camel@localhost.localdomain>
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