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Re: Worse perfomance on 8.2.0 than on 7.4.14

From: Dennis Bjorklund <db(at)zigo(dot)dhs(dot)org>
To: Rolf Østvik <rolfostvik(at)yahoo(dot)no>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Worse perfomance on 8.2.0 than on 7.4.14
Date: 2006-12-31 15:27:12
Message-ID: 4597D6D0.8010902@zigo.dhs.org (view raw or flat)
Thread:
Lists: pgsql-performance
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

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Next:From: Dave CramerDate: 2006-12-31 16:26:53
Subject: Re: Worse perfomance on 8.2.0 than on 7.4.14
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