Date: Tue, 19 Jun 2007 11:50:23 -0400
From: Alvaro Herrera <alvherre@commandprompt.com>
To: Karl Wright <kwright@metacarta.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-performance@postgresql.org
Subject: Re: Performance query about large tables, lots of concurrent access
Message-ID: <20070619155023.GQ4265@alvh.no-ip.org>
References: <4676DD57.7070304@metacarta.com> <14291.1182221811@sss.pgh.pa.us>
	<4677B831.8060704@metacarta.com> <27690.1182263794@sss.pgh.pa.us>
	<4677ECA9.3000402@metacarta.com> <28036.1182264975@sss.pgh.pa.us>
	<4677F617.5000105@metacarta.com>
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User-Agent: Mutt/1.5.13 (2006-08-11)

Karl Wright wrote:

> I did an ANALYZE on that table and repeated the explain, and got this:
> 
> >>>>>>
> metacarta=> analyze intrinsiclink;
> ANALYZE
> metacarta=> explain select count(*) from intrinsiclink where 
> jobid=1181766706097 and 
> childidhash='7E130F3B688687757187F1638D8776ECEF3009E0';
>                                                              QUERY PLAN 
> 
> ------------------------------------------------------------------------------------------------------------------------------------
>  Aggregate  (cost=15276.36..15276.37 rows=1 width=0)
>    ->  Index Scan using i1181764142395 on intrinsiclink 
> (cost=0.00..15255.53 rows=8333 width=0)
>          Index Cond: ((jobid = 1181766706097::bigint) AND 
> ((childidhash)::text = '7E130F3B688687757187F1638D8776ECEF3009E0'::text))
> (3 rows)
> <<<<<<
> 
> ... even more wildly wrong.

Interesting.  What is the statistics target for this table?  Try
increasing it, with ALTER TABLE ... SET STATISTICS, rerun analyze, and
try again.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.