Date: Wed, 13 Aug 2008 16:58:30 -0400
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Chris Kratz <chris.kratz@vistashare.com>
Cc: Decibel! <decibel@decibel.org>, pgsql-performance@postgresql.org
Subject: Re: Incorrect estimates on correlated filters
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Chris Kratz wrote:

> Unfortunately, if I don't think the sorting idea would help in the one case
> I'm looking at which involves filters on two tables that are joined
> together.  The filters happen to be correlated such that about 95% of the
> rows from each filtered table are actually returned after the join.
> Unfortunately, the planner thinks we will get 1 row back.

Maybe you can wrap that part of the query in a SQL function and set its
estimated cost to the real values with ALTER FUNCTION ... ROWS.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support