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From: Terje Elde <terje@elde.net>
To: Jeff Davis <pgsql@j-davis.com>
Cc: Joshua Marsh <icub3d@gmail.com>
Cc: pgsql-performance@postgresql.org
Cc: jim@nasby.net
Subject: Re: Performance With Joins on Large Tables
Date: Wed, 13 Sep 2006 21:42:50 +0200
Message-ID: <45085F3A.1040108@elde.net> (raw)
In-Reply-To: <1158167054.29889.72.camel@dogma.v10.wvs>
References: <38242de90609121517y62517040v8622b9ae93cba23d@mail.gmail.com>
	<20060913064152.GC23173@nasby.net>
	<38242de90609130749u976295fwb10904ff4797b920@mail.gmail.com>
	<1158163655.29889.57.camel@dogma.v10.wvs>
	<38242de90609130919k33208204ka1006ff0ca25f75b@mail.gmail.com>
	<1158167054.29889.72.camel@dogma.v10.wvs>

Jeff Davis wrote:
> Is it overestimating the cost of using indexes or underestimating the
> cost of a seq scan, or both? Maybe explain with the 0.1 setting will
> help?
>   

If enable_seqscan is off, and cost is still set to 100000000, it could 
be that it's quite simply forcibly underestimating the cost of a seqscan 
in this case.

If enable_secscan was off for the mentioned plan, it'd be interesting to 
see if things would be saner with seqscans enabled, and a more 
reasonable random page cost.  If more 'sane' values still produce the 
desired plan, it might be better for other plans etc.

Terje

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