Received: from maia.hub.org (maia-5.hub.org [200.46.204.29]) by mail.postgresql.org (Postfix) with ESMTP id E3F7E1337B68 for ; Tue, 4 Jan 2011 21:24:49 -0400 (AST) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.204.29]) (amavisd-maia, port 10024) with ESMTP id 88680-03 for ; Wed, 5 Jan 2011 01:24:39 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from www.postnewspapers.com.au (www.postnewspapers.com.au [173.230.139.50]) by mail.postgresql.org (Postfix) with ESMTP id D50A91337B64 for ; Tue, 4 Jan 2011 21:24:37 -0400 (AST) Received: from localhost (localhost [127.0.0.1]) by www.postnewspapers.com.au (Postfix) with ESMTP id F1BAA27; Tue, 4 Jan 2011 20:24:36 -0500 (EST) X-Virus-Scanned: amavisd-new at postnewspapers.com.au.com Received: from www.postnewspapers.com.au ([127.0.0.1]) by localhost (www.postnewspapers.com.au [127.0.0.1]) (amavisd-new, port 10024) with LMTP id NGhm5prK1k-f; Tue, 4 Jan 2011 20:24:36 -0500 (EST) Received: from mail.postnewspapers.com.au (ppp171-128.static.internode.on.net [150.101.171.128]) by www.postnewspapers.com.au (Postfix) with ESMTP id 3350819; Tue, 4 Jan 2011 20:24:36 -0500 (EST) Received: from localhost (localhost [127.0.0.1]) by mail.postnewspapers.com.au (Postfix) with ESMTP id 0E3D8AE956; Wed, 5 Jan 2011 09:24:35 +0800 (WST) X-Virus-Scanned: Debian amavisd-new at postnewspapers.com.au Received: from mail.postnewspapers.com.au ([127.0.0.1]) by localhost (mail.postnewspapers.com.au [127.0.0.1]) (amavisd-new, port 10024) with LMTP id i3F-NmPSFnhW; Wed, 5 Jan 2011 09:24:29 +0800 (WST) Received: from [10.1.1.2] (124-168-182-57.dyn.iinet.net.au [124.168.182.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "Craig Ringer", Issuer "POST Certificate Authority" (verified OK)) by mail.postnewspapers.com.au (Postfix) with ESMTPSA id CDEBCAE557; Wed, 5 Jan 2011 09:24:27 +0800 (WST) Message-ID: <4D23C843.8040804@postnewspapers.com.au> Date: Wed, 05 Jan 2011 12:24:19 +1100 From: Craig Ringer User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.13) Gecko/20101209 Fedora/3.1.7-0.35.b3pre.fc14 Thunderbird/3.1.7 MIME-Version: 1.0 To: Fernando Mertins CC: pgsql-performance@postgresql.org Subject: Re: Same stament sometime fast, something slow References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-1.91 tagged_above=-10 required=5 tests=BAYES_00=-1.9, T_RP_MATCHES_RCVD=-0.01 X-Spam-Level: X-Archive-Number: 201101/18 X-Sequence-Number: 41805 On 01/05/2011 05:03 AM, Fernando Mertins wrote: > Hi there, this is my first post. > > I have a PostgreSQL 8.3.6, compiled by Visual C++ build 1400 running on > Windows with virtual machine ^^^^^^^^^^^^^^^^^^^^ What kind of VM host? where? what else is on the same host? Your most likely culprit is I/O contention from other guests on the same host, possibly combined with I/O queuing policies on the host that favour throughput over request latency. Checkpoints might also be a factor. -- Craig Ringer