Date: Tue, 5 Jun 2007 23:38:47 +0200
From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
To: pgsql-performance@postgresql.org
Subject: Re: performance drop on 8.2.4, reverting to 8.1.4
Message-ID: <20070605213847.GA9547@uio.no>
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On Tue, Jun 05, 2007 at 05:30:14PM -0400, Steven Flatt wrote:
> (A) LEFT JOIN (B) ON col WHERE B.col IS NULL
> 
> These queries are much slower on 8.2 than on 8.1 for what looks like the
> reason outlined above.  I have rewritten a few key queries to be of the
> equivalent form:
> 
> (A) WHERE col NOT IN (SELECT col FROM (B))

At least those _can_ be rewritten into a sane form. I have an application
with a large FULL OUTER JOIN, where _both_ sides can return NULLs. (It's
basically a diff between a "current" and a "wanted" state.)

It performs reasonably well under both 8.1 and 8.2, though. Fourteen-table
join or so :-)

/* Steinar */
-- 
Homepage: http://www.sesse.net/