Received: from maia.hub.org (maia-2.hub.org [200.46.204.251]) by mail.postgresql.org (Postfix) with ESMTP id DB80A632F17 for ; Wed, 18 Aug 2010 16:57:11 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.204.251]) (amavisd-maia, port 10024) with ESMTP id 11055-04 for ; Wed, 18 Aug 2010 19:57:03 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from mail-fx0-f46.google.com (mail-fx0-f46.google.com [209.85.161.46]) by mail.postgresql.org (Postfix) with ESMTP id 3DFAD632DD4 for ; Wed, 18 Aug 2010 16:57:03 -0300 (ADT) Received: by fxm13 with SMTP id 13so566834fxm.19 for ; Wed, 18 Aug 2010 12:57:02 -0700 (PDT) Received: by 10.223.121.133 with SMTP id h5mr8311368far.74.1282161422216; Wed, 18 Aug 2010 12:57:02 -0700 (PDT) Received: from Craig-Jamess-MacBook-Pro.local (wsip-70-167-124-126.sd.sd.cox.net [70.167.124.126]) by mx.google.com with ESMTPS id t6sm336865faa.27.2010.08.18.12.56.59 (version=SSLv3 cipher=RC4-MD5); Wed, 18 Aug 2010 12:57:01 -0700 (PDT) Message-ID: <4C6C3B09.6040504@emolecules.com> Date: Wed, 18 Aug 2010 12:56:57 -0700 From: Craig James User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:1.9.1.11) Gecko/20100711 Thunderbird/3.0.6 MIME-Version: 1.0 To: pgsql-performance@postgresql.org Subject: Re: write barrier question References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-1.9 tagged_above=-10 required=5 tests=BAYES_00=-1.9, RCVD_IN_DNSWL_NONE=-0.0001 X-Spam-Level: X-Archive-Number: 201008/204 X-Sequence-Number: 40047 On 8/18/10 12:24 PM, Samuel Gendler wrote: > With barriers off, I saw a transaction rate of about 1200. With > barriers on, it was closer to 1050. The test had a concurrency of 40 > in both cases. I discovered there is roughly 10-20% "noise" in pgbench results after running the exact same test over a 24-hour period on a machine with no other activity. Be sure you run your tests enough times to get good statistics unless you're looking at much larger differences. Craig