From: Tom Lane <tgl@sss.pgh.pa.us>
To: Stelian Iancu <stelian@iancu.ch>
cc: pgsql-performance@postgresql.org
Subject: Re: Slow query (wrong index used maybe)
In-reply-to: <1390833860.7369.75825537.0CAF7BA8@webmail.messagingengine.com>
References: <1390833860.7369.75825537.0CAF7BA8@webmail.messagingengine.com>
Comments: In-reply-to Stelian Iancu <stelian@iancu.ch>
 message dated "Mon, 27 Jan 2014 06:44:20 -0800"
Date: Mon, 27 Jan 2014 10:06:24 -0500
Message-ID: <2631.1390835184@sss.pgh.pa.us>
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Sender: pgsql-performance-owner@postgresql.org

Stelian Iancu <stelian@iancu.ch> writes:
> I have Postrgres 9.3 running on a Linux machine with 32GB RAM. I have a
> fairly large database (some tables with approx. 1 mil. records) and I
> have the following query:
> [ 13-way join joined to a 3-way join ]

Think you'll need to raise join_collapse_limit and from_collapse_limit
to get the best plan here.  The planning time might hurt, though.

TBH that schema looks designed for inefficiency; you'd be better off
rethinking the design rather than hoping the planner is smart enough
to save you from it.

			regards, tom lane


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