Message-ID: <4597D6D0.8010902@zigo.dhs.org>
Date: Sun, 31 Dec 2006 16:27:12 +0100
From: Dennis Bjorklund <db@zigo.dhs.org>
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To: =?ISO-8859-1?Q?Rolf_=D8stvik?= <rolfostvik@yahoo.no>
Cc: pgsql-performance@postgresql.org
Subject: Re: Worse perfomance on 8.2.0 than on 7.4.14
References: <200612311233.10201.rolfostvik@yahoo.no>
In-Reply-To: <200612311233.10201.rolfostvik@yahoo.no>
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Rolf Østvik skrev:

> I have a simple query which uses 32ms on 7.4.14 and 1015ms on 8.2.0.
> I guess 7.4.14 creates a better execution plan than 8.2.0 for this query but


Try to turn off planner options in 8.2 to make it generate the same plan 
as 7.4. Then run EXPLAIN ANALYZE on that query that generate the same 
plan as in 7.4 and we can compare the costs and maybe understand what go 
wrong.

For example, try

set enable_hashjoin to false;
set enable_bitmapscan to false;

but you might need to turn off more things to get it to generate the 7.4 
plan.

/Dennis