Received: from maia.hub.org (maia-5.hub.org [200.46.204.29]) by mail.postgresql.org (Postfix) with ESMTP id DB7041337B4A for ; Wed, 20 Oct 2010 23:26:03 -0300 (ADT) 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 52893-07 for ; Thu, 21 Oct 2010 02:25:58 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from spinlock.commandprompt.com (host-215.commandprompt.net [207.173.203.215]) by mail.postgresql.org (Postfix) with ESMTP id E5AAB1337B5A for ; Wed, 20 Oct 2010 23:25:55 -0300 (ADT) Received: from localhost (localhost [127.0.0.1]) by spinlock.commandprompt.com (Postfix) with ESMTP id 1A35E348017; Wed, 20 Oct 2010 19:25:54 -0700 (PDT) X-Virus-Scanned: Debian amavisd-new at commandprompt.com Received: from spinlock.commandprompt.com ([127.0.0.1]) by localhost (spinlock.commandprompt.com.commandprompt.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id VsaGRJJp8arD; Wed, 20 Oct 2010 19:25:48 -0700 (PDT) Received: from [192.168.1.105] (unknown [75.142.155.118]) by spinlock.commandprompt.com (Postfix) with ESMTPSA id 0CC41348016; Wed, 20 Oct 2010 19:25:46 -0700 (PDT) Subject: Re: BBU Cache vs. spindles From: "Joshua D. Drake" Reply-To: jd@commandprompt.com To: Bruce Momjian Cc: Ben Chobot , Steve Crawford , pgsql-performance@postgresql.org In-Reply-To: <201010210213.o9L2Du210280@momjian.us> References: <201010210213.o9L2Du210280@momjian.us> Content-Type: text/plain; charset="UTF-8" Organization: Command Prompt, Inc. Date: Wed, 20 Oct 2010 19:25:19 -0700 Message-ID: <1287627919.7085.89.camel@jd-desktop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-1.9 tagged_above=-10 required=5 tests=BAYES_00=-1.9 X-Spam-Level: X-Archive-Number: 201010/330 X-Sequence-Number: 40748 On Wed, 2010-10-20 at 22:13 -0400, Bruce Momjian wrote: > Ben Chobot wrote: > > On Oct 7, 2010, at 4:38 PM, Steve Crawford wrote: > > > > > I'm weighing options for a new server. In addition to PostgreSQL, this machine will handle some modest Samba and Rsync load. > > > > > > I will have enough RAM so the virtually all disk-read activity will be cached. The average PostgreSQL read activity will be modest - a mix of single-record and fairly large (reporting) result-sets. Writes will be modest as well but will come in brief (1-5 second) bursts of individual inserts. The rate of insert requests will hit 100-200/second for those brief bursts. > > > > > > So... > > > > > > Am I likely to be better off putting $$$ toward battery-backup on the RAID or toward adding a second RAID-set and splitting off the WAL traffic? Or something else? > > > > A BBU is, what, $100 or so? Adding one seems a no-brainer to me. > > Dedicated WAL spindles are nice and all, but they're still spinning > > media. Raid card cache is waaaay faster, and while it's best at bursty > > writes, it sounds like bursty writes are precisely what you have. > > Totally agree! BBU first, more spindles second. > > -- > Bruce Momjian http://momjian.us > EnterpriseDB http://enterprisedb.com > > + It's impossible for everything to be true. + > -- PostgreSQL.org Major Contributor Command Prompt, Inc: http://www.commandprompt.com/ - 509.416.6579 Consulting, Training, Support, Custom Development, Engineering http://twitter.com/cmdpromptinc | http://identi.ca/commandprompt