Received: from maia.hub.org (maia-4.hub.org [200.46.204.183])
	by mail.postgresql.org (Postfix) with ESMTP id 2C579633C8B
	for <pgsql-performance-postgresql.org@mail.postgresql.org>;
	Thu, 20 May 2010 11:28:26 -0300 (ADT)
Received: from mail.postgresql.org ([200.46.204.86])
	by maia.hub.org (mx1.hub.org [200.46.204.183]) (amavisd-maia,
	port 10024) with ESMTP id 53712-04
	for <pgsql-performance-postgresql.org@mail.postgresql.org>;
	Thu, 20 May 2010 14:28:17 +0000 (UTC)
X-Greylist: from auto-whitelisted by SQLgrey-1.7.6
Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130])
	by mail.postgresql.org (Postfix) with ESMTP id 5A2CF6364B9
	for <pgsql-performance@postgresql.org>;
	Thu, 20 May 2010 11:28:18 -0300 (ADT)
Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1])
	by sss.pgh.pa.us (8.14.2/8.14.2) with ESMTP id o4KESCRN003830;
	Thu, 20 May 2010 10:28:12 -0400 (EDT)
To: Scott Marlowe <scott.marlowe@gmail.com>
cc: Matthew Wakeling <matthew@flymine.org>, pgsql-performance@postgresql.org
Subject: Re: merge join killing performance 
In-reply-to: <AANLkTik0NxYr5FAqlYOqseHhT7WaJv6uJuMvD7ScONnV@mail.gmail.com> 
References: <AANLkTikmwxQJIDfefCoK_SQN2DTwQs1naLwS-RW8PgRU@mail.gmail.com>
	<alpine.DEB.2.00.1005182254110.1867@aragorn.flymine.org>
	<21497.1274287983@sss.pgh.pa.us>
	<AANLkTimfo4qryWUFj6sYRSlQrFZpgLaqB3__Vt0y2Rdl@mail.gmail.com>
	<alpine.DEB.2.00.1005192143570.6090@aragorn.flymine.org>
	<AANLkTilruHtb1cc-TwN_bPVypkhIQo7p8I0y7035xLZ-@mail.gmail.com>
	<AANLkTil5u_ZEPtdVfsl4-XZuieLcXvd9wn5G2jc6k4Eo@mail.gmail.com>
	<AANLkTik0NxYr5FAqlYOqseHhT7WaJv6uJuMvD7ScONnV@mail.gmail.com>
Comments: In-reply-to Scott Marlowe <scott.marlowe@gmail.com>
	message dated "Wed, 19 May 2010 20:07:39 -0600"
Date: Thu, 20 May 2010 10:28:12 -0400
Message-ID: <3829.1274365692@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
X-Virus-Scanned: Maia Mailguard 1.0.1
X-Spam-Status: No, hits=-1.91 tagged_above=-10 required=5 tests=BAYES_00=-1.9,
	T_RP_MATCHES_RCVD=-0.01
X-Spam-Level: 
X-Archive-Number: 201005/112
X-Sequence-Number: 38696

Scott Marlowe <scott.marlowe@gmail.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.

			regards, tom lane