X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (av.hub.org [200.46.204.144]) by postgresql.org (Postfix) with ESMTP id A53279DC86E for ; Tue, 24 Jan 2006 13:07:41 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 44584-09 for ; Tue, 24 Jan 2006 13:07:40 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey- Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by postgresql.org (Postfix) with ESMTP id 51AE59DC9FB for ; Tue, 24 Jan 2006 13:07:38 -0400 (AST) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.13.1/8.13.1) with ESMTP id k0OH7cR7019964; Tue, 24 Jan 2006 12:07:38 -0500 (EST) To: Brad Nicholson cc: pgsql-performance@postgresql.org Subject: Re: Investigating IO Saturation In-reply-to: <43D65736.9020905@ca.afilias.info> References: <43D65736.9020905@ca.afilias.info> Comments: In-reply-to Brad Nicholson message dated "Tue, 24 Jan 2006 11:35:02 -0500" Date: Tue, 24 Jan 2006 12:07:38 -0500 Message-ID: <19963.1138122458@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, score=0.504 required=5 tests=[AWL=-0.309, INFO_TLD=0.813] X-Spam-Score: 0.504 X-Spam-Level: X-Archive-Number: 200601/420 X-Sequence-Number: 16898 Brad Nicholson writes: > I'm investigating a potential IO issue. We're running 7.4 on AIX 5.1. > During periods of high activity (reads, writes, and vacuums), we are > seeing iostat reporting 100% disk usage. I have a feeling that the > iostat numbers are misleading. I can make iostat usage jump from less > than 10% to greater than 95% by running a single vacuum against a > moderate sized table (no noticeable change in the other activity). That's not particularly surprising, and I see no reason to think that iostat is lying to you. More recent versions of PG include parameters that you can use to "throttle" vacuum's I/O demand ... but unthrottled, it's definitely an I/O hog. The vmstat numbers suggest that vacuum is not completely killing you, but you could probably get some improvement in foreground query performance by throttling it back. There are other good reasons to consider an update, anyway. regards, tom lane