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Re: merge join killing performance

From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Matthew Wakeling <matthew(at)flymine(dot)org>, pgsql-performance(at)postgresql(dot)org
Subject: Re: merge join killing performance
Date: 2010-05-20 14:35:37
Message-ID: AANLkTikOp1XVFS1O8j9IiAz95Ihf5Ag9DQvpCSeGwA4G@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-performance
On Thu, May 20, 2010 at 8:28 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> writes:
>> So, Tom, so you think it's possible that the planner isn't noticing
>> all those nulls and thinks it'll just take a row or two to get to the
>> value it needs to join on?
>
> Could be.  I don't have time right now to chase through the code, but
> that sounds like a plausible theory.

K.  I think I'll try an index on that field "where not null" and see
if that helps.

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