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Re: Fwd: 8.2 Query 10 times slower than 8.1 (view-heavy)

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Mark Lewis <mark(dot)lewis(at)mir3(dot)com>
Cc: Evan Carroll <lists(at)evancarroll(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Fwd: 8.2 Query 10 times slower than 8.1 (view-heavy)
Date: 2007-08-31 23:39:25
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
I wrote:
> Mark Lewis <mark(dot)lewis(at)mir3(dot)com> writes:
>> We've been holding back from upgrading to 8.2 because this one is a
>> show-stopper for us.

> Well, you could always make your own version with this patch reverted:
> I might end up doing that in the 8.2 branch if a better solution
> seems too large to back-patch.

I thought of a suitably small hack that should cover at least the main
problem without going so far as to revert that patch entirely.  What we
can do is have the IS NULL estimator recognize when the clause is being
applied at an outer join, and not believe the table statistics in that
case.  I've applied the attached patch for this --- are you interested
in trying it out on your queries before 8.2.5 comes out?

			regards, tom lane

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