Received: from maia.hub.org (unknown [200.46.208.211]) by mail.postgresql.org (Postfix) with ESMTP id 025A3632845 for ; Thu, 11 Feb 2010 12:12:20 -0400 (AST) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.208.211]) (amavisd-maia, port 10024) with ESMTP id 65389-02 for ; Thu, 11 Feb 2010 16:12:01 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-fx0-f228.google.com (mail-fx0-f228.google.com [209.85.220.228]) by mail.postgresql.org (Postfix) with ESMTP id C2EDA63224F for ; Thu, 11 Feb 2010 12:12:09 -0400 (AST) Received: by fxm28 with SMTP id 28so221520fxm.34 for ; Thu, 11 Feb 2010 08:12:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:cc:content-type :content-transfer-encoding; bh=EC4HR2qpWbiOOE0DTAnQ0f4zwRwL+6UsFLkvhMMmNsQ=; b=tvP3K5UPE5ofqDO8Itn2Ex43seNALzbh8EhdZWpkgVcMHLWNsImz8T36nOb/YknYoN cesypBRt3hLMpo3JgDrG9s6duMtDTq3TAlr4ryy8Bx/AouVFlAVCBqpFD4nvOBBOJE8a u7zmBJG9cIz+KreL01sKQor8Fbk33e0qifjfA= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=fONCUrCIuJeJL+uF9lDtUcndNMwdTn28hjMeFhtKaplqcl1+++lHl5/GGY9G1IjQ5y 2RsuyeukmSZ9vtq01zXaAtATEyH1bGAR/W8s5x8tQSIcARE3Nsk2QyCKo2iC8EfvGadx 2cl8OMxOlkHt2OrCYEiqXSdr3wPM8yKnOVWaM= MIME-Version: 1.0 Received: by 10.216.88.8 with SMTP id z8mr10118wee.212.1265904728198; Thu, 11 Feb 2010 08:12:08 -0800 (PST) In-Reply-To: <201002111129.o1BBTK518798@momjian.us> References: <4B7139DD020000250002F0E9@gw.wicourts.gov> <201002111129.o1BBTK518798@momjian.us> Date: Thu, 11 Feb 2010 09:12:08 -0700 Message-ID: Subject: Re: moving pg_xlog -- yeah, it's worth it! From: Scott Marlowe To: Bruce Momjian Cc: Kevin Grittner , Jesper Krogh , pgsql-performance@postgresql.org 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=-2.478 tagged_above=-10 required=5 tests=AWL=0.121, BAYES_00=-2.599 X-Spam-Level: X-Archive-Number: 201002/186 X-Sequence-Number: 37607 On Thu, Feb 11, 2010 at 4:29 AM, Bruce Momjian wrote: > Kevin Grittner wrote: >> Jesper Krogh wrote: >> >> > Sorry if it is obvious.. but what filesystem/OS are you using and >> > do you have BBU-writeback on the main data catalog also? >> >> Sorry for not providing more context. >> >> ATHENA:/var/pgsql/data # uname -a >> Linux ATHENA 2.6.16.60-0.39.3-smp #1 SMP Mon May 11 11:46:34 UTC >> 2009 x86_64 x86_64 x86_64 GNU/Linux >> ATHENA:/var/pgsql/data # cat /etc/SuSE-release >> SUSE Linux Enterprise Server 10 (x86_64) >> VERSION =3D 10 >> PATCHLEVEL =3D 2 >> >> File system is xfs noatime,nobarrier for all data; OS is on ext3. =A0I >> *think* the pg_xlog mirrored pair is hanging off the same >> BBU-writeback controller as the big RAID, but I'd have to track down >> the hardware tech to confirm, and he's out today. =A0System has 16 >> Xeon CPUs and 64 GB RAM. > > I would be surprised if the RAID controller had a BBU-writeback cache. > I don't think having xlog share a BBU-writeback makes things slower, and > if it does, I would love for someone to explain why. I believe in the past when this discussion showed up it was mainly due to them being on the same file system (and then not with pg_xlog separate) that made the biggest difference. I recall there being a noticeable performance gain from having two file systems on the same logical RAID device even.