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Re: Performance problem on 8.2.4, but not 8.2.3

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Steinar H(dot) Gunderson" <sgunderson(at)bigfoot(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Performance problem on 8.2.4, but not 8.2.3
Date: 2007-05-25 20:33:46
Message-ID: 21464.1180125226@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
"Steinar H. Gunderson" <sgunderson(at)bigfoot(dot)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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Subject: Re: Performance problem on 8.2.4, but not 8.2.3
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