X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org
Received: from localhost (av.hub.org [200.46.204.144])
	by postgresql.org (Postfix) with ESMTP id 32E8F9DCAD2
	for <pgsql-performance-postgresql.org@localhost.postgresql.org>;
	Fri, 20 Jan 2006 12:35:00 -0400 (AST)
Received: from postgresql.org ([200.46.204.71])
	by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024)
	with ESMTP id 02029-08
	for <pgsql-performance-postgresql.org@localhost.postgresql.org>;
	Fri, 20 Jan 2006 12:34:55 -0400 (AST)
X-Greylist: from auto-whitelisted by SQLgrey-
Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130])
	by postgresql.org (Postfix) with ESMTP id 343AA9DCAD0
	for <pgsql-performance@postgresql.org>;
	Fri, 20 Jan 2006 12:34:54 -0400 (AST)
Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1])
	by sss.pgh.pa.us (8.13.1/8.13.1) with ESMTP id k0KGYnB1018685;
	Fri, 20 Jan 2006 11:34:49 -0500 (EST)
To: Bruce Momjian <pgman@candle.pha.pa.us>
cc: Simon Riggs <simon@2ndquadrant.com>,
	=?ISO-8859-1?Q?Jean-Philippe_C=F4t=E9?=
	<jean-philippe.cote@crt.umontreal.ca>, pgsql-performance@postgresql.org
Subject: Re: Extremely irregular query performance 
In-reply-to: <200601201619.k0KGJWE19919@candle.pha.pa.us> 
References: <200601201619.k0KGJWE19919@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
	message dated "Fri, 20 Jan 2006 11:19:32 -0500"
Date: Fri, 20 Jan 2006 11:34:49 -0500
Message-ID: <18684.1137774889@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
X-Virus-Scanned: by amavisd-new at hub.org
X-Spam-Status: No, score=0.094 required=5 tests=[AWL=0.094]
X-Spam-Score: 0.094
X-Spam-Level: 
X-Archive-Number: 200601/341
X-Sequence-Number: 16819

Bruce Momjian <pgman@candle.pha.pa.us> writes:
>     <para>
> !    Genetic query optimization (<acronym>GEQO</acronym>) randomly 
> !    tests execution plans.  Therefore, when the number of tables 
> !    exceeds <varname>geqo</> and genetic query optimization is in use,
> !    the execution plan will change each time the statement is executed.
>     </para>

geqo_threshold, please --- geqo is a boolean.

Possibly better wording:  Therefore, when the number of tables exceeds
geqo_threshold causing genetic query optimization to be used, the
execution plan is likely to change each time the statement is executed.

			regards, tom lane