Received: from localhost (unknown [200.46.204.183]) by mail.postgresql.org (Postfix) with ESMTP id E72B165058C for ; Tue, 25 Nov 2008 00:48:41 -0400 (AST) Received: from mail.postgresql.org ([200.46.204.86]) by localhost (mx1.hub.org [200.46.204.183]) (amavisd-maia, port 10024) with ESMTP id 27900-01-2 for ; Tue, 25 Nov 2008 00:48:39 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from westnet.com (westnet.com [216.187.52.2]) by mail.postgresql.org (Postfix) with ESMTP id B76936505BC for ; Tue, 25 Nov 2008 00:40:56 -0400 (AST) Received: from westnet.com (localhost [127.0.0.1]) by westnet.com (8.14.0/8.14.0) with ESMTP id mAP4eqpO003378; Mon, 24 Nov 2008 23:40:52 -0500 (EST) Received: from localhost (gsmith@localhost) by westnet.com (8.14.0/8.13.2/Submit) with ESMTP id mAP4eqJB003372; Mon, 24 Nov 2008 23:40:52 -0500 (EST) X-Authentication-Warning: westnet.com: gsmith owned process doing -bs Date: Mon, 24 Nov 2008 23:40:52 -0500 (EST) From: Greg Smith X-X-Sender: gsmith@westnet.com To: Scott Marlowe cc: Brad Nicholson , Kevin Kempter , pgsql-performance@postgresql.org Subject: Re: Monitoring buffercache... In-Reply-To: Message-ID: References: <200811241143.57182.kevin@kevinkempterllc.com> <1227556326.18990.98.camel@bnicholson-desktop> 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: 200811/251 X-Sequence-Number: 31982 On Mon, 24 Nov 2008, Scott Marlowe wrote: > My guess is that the period of time for which pg_buffercache takes locks > on the buffer map are short enough that it isn't a real big deal on a > fast enough server. As the server involved gets faster, the amount of time the locks are typically held for drops. As your shared_buffers allocation increases, that amount of time goes up. So how painful the overhead is depends on how fast your CPU is relative to how much memory is in it. Since faster systems tend to have more RAM in them, too, it's hard to say whether the impact will be noticable. Also, noting that the average case isn't impacted much isn't the concern here. The problem is how much having all partition locks held will increase impact worst-case latency. -- * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD