Received: from localhost (maia-5.hub.org [200.46.204.182]) by postgresql.org (Postfix) with ESMTP id A27509FB1CC for ; Thu, 12 Jul 2007 00:10:45 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.182]) (amavisd-maia, port 10024) with ESMTP id 44990-02 for ; Thu, 12 Jul 2007 00:10:38 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.5 Received: from westnet.com (westnet.com [216.187.52.2]) by postgresql.org (Postfix) with ESMTP id 8991B9FB47B for ; Thu, 12 Jul 2007 00:10:41 -0300 (ADT) Received: from westnet.com (localhost [127.0.0.1]) by westnet.com (8.14.0/8.14.0) with ESMTP id l6C3AbXn020690 for ; Wed, 11 Jul 2007 23:10:37 -0400 (EDT) Received: from localhost (gsmith@localhost) by westnet.com (8.14.0/8.13.2/Submit) with ESMTP id l6C3AaZc020687 for ; Wed, 11 Jul 2007 23:10:36 -0400 (EDT) X-Authentication-Warning: westnet.com: gsmith owned process doing -bs Date: Wed, 11 Jul 2007 23:10:36 -0400 (EDT) From: Greg Smith X-X-Sender: gsmith@westnet.com To: pgsql-performance@postgresql.org Subject: Estimating WAL volume Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200707/130 X-Sequence-Number: 25814 All this talk of WAL writing lately has me wondering something I haven't spent enough time looking at the source to figure out myself this week...any good rules of thumb out there for estimating WAL volume? I'm used to just measuring it via benchmarking but it strikes me a formula would be nice to have for pre-planning. For example, if I have a table where a typical row is X bytes wide, and I'm updating Y of those per second, what's the expected write rate of WAL volume? Some % of those writes are going to be full pages; what's typical? How much does the number and complexity of indexes factor into things--just add the width of the index in bytes to the size of the record, or is it worse than that? -- * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD