Date: Wed, 27 Sep 2006 15:13:50 -0500
From: "Jim C. Nasby" <jim@nasby.net>
To: Dave Dutcher <dave@tridecap.com>
Cc: 'Tim Truman' <tim@advam.com>, pgsql-performance@postgresql.org
Subject: Re: Forcing the use of particular execution plans
Message-ID: <20060927201350.GS19827@nasby.net>
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On Wed, Sep 27, 2006 at 10:51:26AM -0500, Dave Dutcher wrote:
> To make the planner prefer an index scan over a seq scan, I would first
> check the statistics again, and then you can try setting enable_seqscan to
> false (enable_seqscan is meant more for testing than production) or, you
> could try reducing random_page_cost, but you should test that against a
> range of queries before putting it in production.

Index scans are also pretty picky about correlation. If you have really
low correlation you don't want to index scan, but I think our current
estimates make it too eager to switch to a seqscan.
-- 
Jim Nasby                                            jim@nasby.net
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)