X-Original-To: pgsql-performance-postgresql.org@postgresql.org Received: from localhost (wm.hub.org [200.46.204.128]) by postgresql.org (Postfix) with ESMTP id C6CD99FABE7 for ; Tue, 12 Sep 2006 21:15:31 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.128]) (amavisd-new, port 10024) with ESMTP id 81540-07 for ; Wed, 13 Sep 2006 00:15:23 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey- Received: from linda-4.paradise.net.nz (linda-4.paradise.net.nz [203.96.152.183]) by postgresql.org (Postfix) with ESMTP id CBFB99FA50F for ; Tue, 12 Sep 2006 21:15:22 -0300 (ADT) Received: from smtp-2.paradise.net.nz (tclsnelb1-src-1.paradise.net.nz [203.96.152.172]) by linda-4.paradise.net.nz (Paradise.net.nz) with ESMTP id <0J5I008908PJUF@linda-4.paradise.net.nz> for pgsql-performance@postgresql.org; Wed, 13 Sep 2006 12:15:20 +1200 (NZST) Received: from [192.168.1.11] (218-101-29-47.dsl.clear.net.nz [218.101.29.47]) by smtp-2.paradise.net.nz (Postfix) with ESMTP id 8E1AA110D1DA; Wed, 13 Sep 2006 12:15:19 +1200 (NZST) Date: Wed, 13 Sep 2006 12:14:52 +1200 From: Mark Kirkwood Subject: Re: Poor performance on seq scan In-reply-to: <45072B61.3080506@designaproduct.biz> To: Laszlo Nagy Cc: pgsql-performance@postgresql.org Message-id: <45074D7C.8000907@paradise.net.nz> MIME-version: 1.0 Content-type: text/plain; format=flowed; charset=ISO-8859-1 Content-transfer-encoding: 7bit User-Agent: Thunderbird 1.5.0.4 (X11/20060704) References: <450684EC.4090304@designaproduct.biz> <17034.1158079926@sss.pgh.pa.us> <45072130.6020508@modgraph-usa.com> <45072B61.3080506@designaproduct.biz> X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0 tagged_above=0 required=5 tests= X-Spam-Level: X-Archive-Number: 200609/108 X-Sequence-Number: 20794 Laszlo Nagy wrote: > Craig A. James wrote: >> >> There IS a bug for SATA disk drives in some versions of the Linux >> kernel. On a lark I ran some of the I/O tests in this thread, and >> much to my surprise discovered my write speed was 6 MB/sec ... ouch! >> On an identical machine, different kernel, the write speed was 54 MB/sec. > My disks are running in SATA150 mode. Whatever it means. > > I'm using FreeBSD, and not just because it dynamically alters the > priority of long running processes. :-) > I dunno if this has been suggested, but try changing the sysctl vfs.read_max. The default is 8 and results in horrible RAID performance (having said that, not sure if RAID1 is effected, only striped RAID levels...), anyway try 16 or 32 and see if you seq IO rate improves at all (tho the underlying problem does look like a poor SATA chipset/driver combination). I also found that building your ufs2 filesystems with 32K blocks and 4K fragments improved sequential performance considerably (even for 8K reads). Cheers Mark