Received: from localhost (unknown [200.46.204.183]) by postgresql.org (Postfix) with ESMTP id F0CA264FCF3 for ; Wed, 10 Sep 2008 11:49:20 -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 85798-01-2 for ; Wed, 10 Sep 2008 11:49:13 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from westnet.com (westnet.com [216.187.52.2]) by postgresql.org (Postfix) with ESMTP id 7101764FCF4 for ; Wed, 10 Sep 2008 11:49:12 -0300 (ADT) Received: from westnet.com (localhost [127.0.0.1]) by westnet.com (8.14.0/8.14.0) with ESMTP id m8AEn6hm025413; Wed, 10 Sep 2008 10:49:06 -0400 (EDT) Received: from localhost (gsmith@localhost) by westnet.com (8.14.0/8.13.2/Submit) with ESMTP id m8AEn60b025410; Wed, 10 Sep 2008 10:49:06 -0400 (EDT) X-Authentication-Warning: westnet.com: gsmith owned process doing -bs Date: Wed, 10 Sep 2008 10:49:06 -0400 (EDT) From: Greg Smith X-X-Sender: gsmith@westnet.com To: Mark Wong cc: "pgsql-performance@postgresql.org" , Gabrielle Roth , Selena Deckelmann Subject: Re: Effects of setting linux block device readahead size In-Reply-To: <70c01d1d0809092353r4ae687a3ycf3d99d43a5680cf@mail.gmail.com> Message-ID: References: <70c01d1d0809092353r4ae687a3ycf3d99d43a5680cf@mail.gmail.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed 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: 200809/105 X-Sequence-Number: 31418 On Tue, 9 Sep 2008, Mark Wong wrote: > I've started to display the effects of changing the Linux block device > readahead buffer to the sequential read performance using fio. Ah ha, told you that was your missing tunable. I'd really like to see the whole table of one disk numbers re-run when you get a chance. The reversed ratio there on ext2 (59MB read/92MB write) was what tipped me off that something wasn't quite right initially, and until that's fixed it's hard to analyze the rest. Based on your initial data, I'd say that the two useful read-ahead settings for this system are 1024KB (conservative but a big improvement) and 8192KB (point of diminishing returns). The one-disk table you've got (labeled with what the default read-ahead is) and new tables at those two values would really flesh out what each disk is capable of. -- * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD