From: Tom Lane <tgl@sss.pgh.pa.us>
To: Steinar H. Gunderson <sgunderson@bigfoot.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Performance problem on 8.2.4, but not 8.2.3
Date: Fri, 25 May 2007 16:33:46 -0400
Message-ID: <21464.1180125226@sss.pgh.pa.us> (raw)
In-Reply-To: <20070525200523.GA15547@uio.no>
References: <2C91A79B-6AFD-4734-B245-2ED81F4F15D4@mediamatters.org>
<21071.1180122995@sss.pgh.pa.us>
<20070525200523.GA15547@uio.no>
"Steinar H. Gunderson" <sgunderson@bigfoot.com> writes:
> It looks like the estimated cost is lower for 8.2.4 -- could it be that the
> fact that he's giving it more memory lead to the planner picking a plan that
> happens to be worse?
Offhand I don't think so. More work_mem might make a hash join look
cheaper (or a sort for a mergejoin), but the problem here seems to be
that it's switching away from a hash and to a nestloop. Which is a
loser because there are many more outer-relation rows than it's
expecting.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, sgunderson@bigfoot.com
Subject: Re: Performance problem on 8.2.4, but not 8.2.3
In-Reply-To: <21464.1180125226@sss.pgh.pa.us>
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