Re: Performance With Joins on Large Tables

From: Terje Elde <terje(at)elde(dot)net>
To: Jeff Davis <pgsql(at)j-davis(dot)com>
Cc: Joshua Marsh <icub3d(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org, jim(at)nasby(dot)net
Subject: Re: Performance With Joins on Large Tables
Date: 2006-09-13 19:42:50
Message-ID: 45085F3A.1040108@elde.net
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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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