Date: Thu, 19 Oct 2006 12:22:50 -0500
From: "Jim C. Nasby" <jim@nasby.net>
To: Richard Huxton <dev@archonet.com>
Cc: Jens Schipkowski <jens.schipkowski@apus.co.at>,
	pgsql-performance@postgresql.org
Subject: Re: DB Performance decreases due to often written/accessed
Message-ID: <20061019172249.GT71084@nasby.net>
References: <op.thn5e4sj81rjf6@xjens.apus.local>
	<453791E6.4020600@archonet.com>
	<op.thohq8zj81rjf6@xjens.apus.local>
	<4537B394.9000205@archonet.com>
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On Thu, Oct 19, 2006 at 06:19:16PM +0100, Richard Huxton wrote:
> OK - these plans look about the same, but the time is greatly different. 
> Both have rows=140247 as the estimated number of rows in tbl_reg. Either 
>  you have many more rows in the second case (in which case you're not 
> running ANALYSE enough) or you have lots of gaps in the table (you're 
> not running VACUUM enough).
 
Look closer... the actual stats show that the sorts in the second case
are returning far more rows. And yes, analyze probably needs to happen.

> I'd then try putting an index on (attr1,attr2,attr3...attr6) and see if 
> that helps reduce time.

With bitmap index scans, I think it'd be much better to create 6 indexes
and see which ones actually get used (and then drop the others).
-- 
Jim Nasby                                            jim@nasby.net
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)