Received: from localhost (unknown [200.46.204.183]) by postgresql.org (Postfix) with ESMTP id CF60064FCF2 for ; Fri, 12 Sep 2008 05:38:58 -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 62096-09 for ; Fri, 12 Sep 2008 05:38:51 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from mail.mnc.ch (62-2-77-205.static.cablecom.ch [62.2.77.205]) by postgresql.org (Postfix) with ESMTP id D698A64FCD7 for ; Fri, 12 Sep 2008 05:38:49 -0300 (ADT) Received: from localhost (mail2.mnc.ch [127.0.0.1]) by mail.mnc.ch (Postfix) with ESMTP id 6419B23081; Fri, 12 Sep 2008 08:38:46 +0000 (GMT) X-Virus-Scanned: amavisd-new at mnc.ch Received: from mail.mnc.ch ([127.0.0.1]) by localhost (mail2.mnc.ch [127.0.0.1]) (amavisd-new, port 10025) with ESMTP id 1p+wdJTTA5Mg; Fri, 12 Sep 2008 08:38:46 +0000 (GMT) Received: from meuh.localdomain (62-2-77-204.static.cablecom.ch [62.2.77.204]) by mail.mnc.ch (Postfix) with ESMTP id F34292307A; Fri, 12 Sep 2008 08:38:45 +0000 (GMT) Received: by meuh.localdomain (Postfix, from userid 1000) id C3596183754; Fri, 12 Sep 2008 10:38:45 +0200 (CEST) To: Craig James Cc: pgsql-performance@postgresql.org Subject: Re: Choosing a filesystem References: <48C94770.2090505@shopzeus.com> <20080911172332.GP6714@it.is.rice.edu> <48C90F58.EE98.0025.0@wicourts.gov> <48C959BD.80307@shopzeus.com> <48C97740.9040404@emolecules.com> From: Guillaume Cottenceau X-Hashcash: 1:20:080912:craig_james@emolecules.com::+Rnj57x4IDS3OqWs:000000000000000000000000000000000000fyj X-Hashcash: 1:20:080912:pgsql-performance@postgresql.org::/7weCnGW2mbaHPM2:0000000000000000000000000000039Fc Date: Fri, 12 Sep 2008 10:38:45 +0200 In-Reply-To: <48C97740.9040404@emolecules.com> (Craig James's message of "Thu\, 11 Sep 2008 12\:53\:36 -0700") Message-ID: <873ak5iwru.fsf@mnc.ch> User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii 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: 200809/160 X-Sequence-Number: 31473 Craig James writes: > The performance improvement of a BB cache is amazing. Could some of you share the insight on why this is the case? I cannot find much information on it on wikipedia, for example. Even http://linuxfinances.info/info/diskusage.html doesn't explain *why*. Out of the blue, is it just because when postgresql fsync's after a write, on a normal system the write has to really happen on disk and waiting for it to be complete, whereas with BBU cache the fsync is almost immediate because the write cache actually replaces the "really on disk" write? -- Guillaume Cottenceau, MNC Mobile News Channel SA, an Alcatel-Lucent Company Av. de la Gare 10, 1003 Lausanne, Switzerland - direct +41 21 317 50 36