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Re: Weird 8.2.4 performance

From: Richard Huxton <dev(at)archonet(dot)com>
To: Mark Kirkwood <markir(at)paradise(dot)net(dot)nz>
Cc: Kurt Overberg <kurt(at)hotdogrecords(dot)com>,pgsql-performance(at)postgresql(dot)org
Subject: Re: Weird 8.2.4 performance
Date: 2007-06-07 09:23:19
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
Mark Kirkwood wrote:
> 8.2 is deciding to use a bitmap index scan on taskid_taskinstance_key, 
> which seems to be slower (!) than a plain old index scan that 8.0 is 
> using. A dirty work around is to disable bitmap scans via:

I'm having difficulty figuring out why it's doing this at all. There's 
only one index involved, and it's over the primary-key to boot!

An EXPLAIN ANALYSE with enable_bitmapscan off should say why PG thinks 
the costs are cheaper than they actually are.

PS - well worded question Kurt. All the relevant information neatly laid 
out, explain analyse on both platforms - you should be charging to let 
people help ;-)

   Richard Huxton
   Archonet Ltd

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