Received: from maia.hub.org (maia-2.hub.org [200.46.204.251]) by mail.postgresql.org (Postfix) with ESMTP id 313F41337B8C for ; Mon, 31 Jan 2011 12:49:54 -0400 (AST) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.204.251]) (amavisd-maia, port 10024) with ESMTP id 46159-02 for ; Mon, 31 Jan 2011 16:49:46 +0000 (UTC) X-Greylist: delayed 00:05:33.749089 by SQLgrey-1.7.6 Received: from mx01.bfk.de (mx01.bfk.de [193.227.124.2]) by mail.postgresql.org (Postfix) with ESMTP id 7A8B31337B8A for ; Mon, 31 Jan 2011 12:49:46 -0400 (AST) Received: from mx00.int.bfk.de ([10.119.110.2]) by mx01.bfk.de with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) id 1PjwrH-0004r2-EJ; Mon, 31 Jan 2011 16:44:07 +0000 Received: by bfk.de with local id 1PjwrH-00084j-A2; Mon, 31 Jan 2011 16:44:07 +0000 To: "Mark Felder" Cc: pgsql-performance@postgresql.org Subject: Re: Any experience using "shake" defragmenter? References: <4D45C607.4070101@vmsinfo.com> From: Florian Weimer Date: Mon, 31 Jan 2011 16:44:07 +0000 In-Reply-To: (Mark Felder's message of "Sun\, 30 Jan 2011 15\:31\:26 -0600") Message-ID: <82k4hl81m0.fsf@mid.bfk.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-1.91 tagged_above=-10 required=5 tests=BAYES_00=-1.9, T_RP_MATCHES_RCVD=-0.01 X-Spam-Level: X-Archive-Number: 201101/343 X-Sequence-Number: 42130 * Mark Felder: > Why do you feel the need to defrag your *nix box? Some file systems (such as XFS) read the whole extent list into RAM when a file is opened. When the extend list is long due to fragmentation, this can take a *long* time (in the order of minutes with multi-gigabyte Oracle Berkeley DB files). This phenomenon is less pronounced with PostgreSQL because it splits large relations into one-gigabyte chunks, and it writes the files sequentally. But a small effect is probably still there. --=20 Florian Weimer BFK edv-consulting GmbH http://www.bfk.de/ Kriegsstra=DFe 100 tel: +49-721-96201-1 D-76133 Karlsruhe fax: +49-721-96201-99