Received: from localhost (unknown [200.46.204.183]) by postgresql.org (Postfix) with ESMTP id 8F02C64FCD2 for ; Thu, 11 Sep 2008 02:56:46 -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 91986-06 for ; Thu, 11 Sep 2008 02:56:43 -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 C103664FCFE for ; Thu, 11 Sep 2008 02:56:43 -0300 (ADT) Received: from westnet.com (localhost [127.0.0.1]) by westnet.com (8.14.0/8.14.0) with ESMTP id m8B5ueUF004822; Thu, 11 Sep 2008 01:56:40 -0400 (EDT) Received: from localhost (gsmith@localhost) by westnet.com (8.14.0/8.13.2/Submit) with ESMTP id m8B5ueGW004816; Thu, 11 Sep 2008 01:56:40 -0400 (EDT) X-Authentication-Warning: westnet.com: gsmith owned process doing -bs Date: Thu, 11 Sep 2008 01:56:40 -0400 (EDT) From: Greg Smith X-X-Sender: gsmith@westnet.com To: James Mansion cc: pgsql-performance@postgresql.org Subject: Re: Effects of setting linux block device readahead size In-Reply-To: <48C8AACD.5090702@mansionfamily.plus.com> Message-ID: References: <70c01d1d0809092353r4ae687a3ycf3d99d43a5680cf@mail.gmail.com> <48C8AACD.5090702@mansionfamily.plus.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: 200809/130 X-Sequence-Number: 31443 On Thu, 11 Sep 2008, James Mansion wrote: > Most spinning disks now are nearer to 100MB/s streaming. You've talked > yourself into twice that, random access! The point I was trying to make there is that even under impossibly optimal circumstances, you'd be hard pressed to blow out the disk's read cache with seek-dominated data even if you read a lot at each seek point. That idea didn't make it from my head into writing very well though. -- * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD