Received: from localhost (unknown [200.46.208.211]) by mail.postgresql.org (Postfix) with ESMTP id F099763619C for ; Wed, 25 Mar 2009 00:51:41 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by localhost (mx1.hub.org [200.46.208.211]) (amavisd-maia, port 10024) with ESMTP id 14511-10 for ; Wed, 25 Mar 2009 00:51:38 -0300 (ADT) X-Greylist: delayed 00:30:35.046342 by SQLgrey-1.7.6 Received: from smtp4.clear.net.nz (smtp4.clear.net.nz [203.97.37.64]) by mail.postgresql.org (Postfix) with ESMTP id 53936633719 for ; Wed, 25 Mar 2009 00:51:34 -0300 (ADT) Received: from zmori.markir.net (121-73-175-180.dsl.telstraclear.net [121.73.175.180]) by smtp4.clear.net.nz (CLEAR Net Mail) with ESMTP id <0KH1005IILASST20@smtp4.clear.net.nz> for pgsql-performance@postgresql.org; Wed, 25 Mar 2009 16:20:56 +1300 (NZDT) Date: Wed, 25 Mar 2009 16:20:52 +1300 From: Mark Kirkwood Subject: Re: Raid 10 chunksize In-reply-to: To: Scott Marlowe Cc: "pgsql-performance@postgresql.org" Message-id: <49C9A314.6050302@paradise.net.nz> MIME-version: 1.0 Content-type: text/plain; charset=ISO-8859-1; format=flowed Content-transfer-encoding: 7bit References: <49C98433.5080709@paradise.net.nz> User-Agent: Thunderbird 2.0.0.19 (X11/20090117) 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: 200903/363 X-Sequence-Number: 33285 Scott Marlowe wrote: > On Tue, Mar 24, 2009 at 7:09 PM, Mark Kirkwood wrote: > >> I'm trying to pin down some performance issues with a machine where I work, >> we are seeing (read only) query response times blow out by an order of >> magnitude or more at busy times. Initially we blamed autovacuum, but after a >> tweak of the cost_delay it is *not* the problem. Then I looked at >> checkpoints... and altho there was some correlation with them and the query >> response - I'm thinking that the raid chunksize may well be the issue. >> > > Sounds to me like you're mostly just running out of bandwidth on your > RAID array. Whether or not you can tune it to run faster is the real > issue. This problem becomes worse as you add clients and the RAID > array starts to thrash. Thrashing is likely to be worse with a small > chunk size, so that's definitely worth a look at fixing. > > Yeah, I was wondering if we are maxing out the bandwidth... >> Fortunately there is an identical DR box, so I could do a little testing. >> > > Can you try changing the chunksize on the test box you're testing on > to see if that helps? > > Yes - or I am hoping to anyway (part of posting here was to collect some outside validation for the idea). Thanks for your input! Cheers Mark