Received: from localhost (unknown [200.46.204.184]) by developer.postgresql.org (Postfix) with ESMTP id BCCFF2E005F for ; Wed, 16 Apr 2008 16:56:00 -0300 (ADT) Received: from developer.postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.184]) (amavisd-maia, port 10024) with ESMTP id 72109-07 for ; Wed, 16 Apr 2008 16:55:49 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.5 Received: from westnet.com (westnet.com [216.187.52.2]) by developer.postgresql.org (Postfix) with ESMTP id B60BE2E0030 for ; Wed, 16 Apr 2008 16:55:52 -0300 (ADT) Received: from westnet.com (localhost [127.0.0.1]) by westnet.com (8.14.0/8.14.0) with ESMTP id m3GJtp8u009690 for ; Wed, 16 Apr 2008 15:55:51 -0400 (EDT) Received: from localhost (gsmith@localhost) by westnet.com (8.14.0/8.13.2/Submit) with ESMTP id m3GJtp8w009685 for ; Wed, 16 Apr 2008 15:55:51 -0400 (EDT) X-Authentication-Warning: westnet.com: gsmith owned process doing -bs Date: Wed, 16 Apr 2008 15:55:51 -0400 (EDT) From: Greg Smith X-X-Sender: gsmith@westnet.com To: pgsql-performance@postgresql.org Subject: Re: Background writer underemphasized ... In-Reply-To: <20080416144335.04368b67.wmoran@collaborativefusion.com> Message-ID: References: <480619CA.2080904@geizhals.at> <20080416144335.04368b67.wmoran@collaborativefusion.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200804/210 X-Sequence-Number: 29703 On Wed, 16 Apr 2008, Bill Moran wrote: >> bgwriter_delay = 10000ms # 10-10000ms between rounds >> bgwriter_lru_maxpages = 1000 # 0-1000 max buffers written/round > Have you watched closely under load to ensure that you're not seeing a > huge performance hit every 10s when the bgwriter kicks off? bgwriter_lru_maxpages = 1000 means that any background writer pass can write at most 1000 pages = 8MB. Those are buffered writes going into the OS cache, which it will write out at its own pace later. That isn't going to cause a performance hit when it happens. That isn't the real mystery though--where's the RAID5 rant I was expecting from you? -- * Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD