Received: from localhost (unknown [200.46.204.183]) by postgresql.org (Postfix) with ESMTP id B04F637BEB5; Mon, 29 Sep 2008 04:02:03 -0300 (ADT) Received: from postgresql.org ([200.46.204.86]) by localhost (mx1.hub.org [200.46.204.183]) (amavisd-maia, port 10024) with ESMTP id 56866-09; Mon, 29 Sep 2008 04:01:59 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from smtp-out1.tiscali.nl (smtp-out1.tiscali.nl [195.241.79.176]) by postgresql.org (Postfix) with ESMTP id 3B94D37BD93; Mon, 29 Sep 2008 04:01:58 -0300 (ADT) Received: from [195.240.247.225] (helo=mx1.joris2k.local) by smtp-out1.tiscali.nl with esmtp id 1KkClY-0007Na-Pk; Mon, 29 Sep 2008 09:01:56 +0200 Received: from localhost (localhost [127.0.0.1]) by mx1.joris2k.local (Postfix) with ESMTP id 941704008D; Mon, 29 Sep 2008 09:03:16 +0200 (CEST) X-Virus-Scanned: E-mail scanned by amavisd-new at familiedobbelsteen.nl (mx1.joris2k.local) Received: from mx1.joris2k.local ([127.0.0.1]) by localhost (mx1.joris2k.local [127.0.0.1]) (amavisd-new, port 10024) with LMTP id NteXknW8EI6A; Mon, 29 Sep 2008 09:02:57 +0200 (CEST) Received: from exchange1.joris2k.local (exchange1.joris2k.local [192.168.10.45]) by mx1.joris2k.local (Postfix) with ESMTP id D3AFB40087; Mon, 29 Sep 2008 09:02:57 +0200 (CEST) Received: from [192.168.10.241] ([192.168.10.241] RDNS failed) by exchange1.joris2k.local over TLS secured channel with Microsoft SMTPSVC(6.0.3790.3959); Mon, 29 Sep 2008 08:01:35 +0100 Message-ID: <48E07D38.90906@familiedobbelsteen.nl> Date: Mon, 29 Sep 2008 09:01:12 +0200 From: Joris Dobbelsteen User-Agent: Thunderbird 2.0.0.17 (X11/20080925) MIME-Version: 1.0 To: Matthew Pulis CC: pgsql-admin@postgresql.org, pgsql-general@postgresql.org Subject: Re: [GENERAL] PostgreSQL Cache References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 29 Sep 2008 07:01:35.0542 (UTC) FILETIME=[36242560:01C92201] X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0 tagged_above=0 required=5 tests=none X-Spam-Level: X-Archive-Number: 200809/325 X-Sequence-Number: 30418 Matthew Pulis wrote: > Hi, > > I need to perform some timed testing, thus need to make sure that disk > cache does not affect me. Is clearing the OS (Ubuntu) disk cache, ( by > running: sudo echo 3 | sudo tee /proc/sys/vm/drop_caches ) enough to > do this? If not can you please point me to some site please since all > I am finding is such command. Look for methodologies for doing performance tests. A problem is that the disk cache is an essential part that makes up for postgresql performance. Also do not forget about overhead and inaccuracies that you will affect your results. In general performance tests are a rather large simulation of how your application would use the database. It should be large enough for many effects (such as initial cache state) to be neglected. It only provides an average for the performance on your system configuration. If you run it a few times more, you can compute the variation. It provides some insight how stable your system is in handling the workload. - Joris