Received: from maia.hub.org (maia-2.hub.org [200.46.204.251]) by mail.postgresql.org (Postfix) with ESMTP id 543D51337B2F for ; Fri, 21 Jan 2011 15:50:57 -0400 (AST) 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 61879-10 for ; Fri, 21 Jan 2011 19:50:50 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by mail.postgresql.org (Postfix) with ESMTP id B21891336FA7 for ; Fri, 21 Jan 2011 15:50:49 -0400 (AST) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.14.2/8.14.2) with ESMTP id p0LJolLM017637; Fri, 21 Jan 2011 14:50:47 -0500 (EST) To: grant@amadensor.com cc: pgsql-performance@postgresql.org Subject: Re: Fun little performance IMPROVEMENT... In-reply-to: References: Comments: In-reply-to grant@amadensor.com message dated "Fri, 21 Jan 2011 11:12:35 -0700" Date: Fri, 21 Jan 2011 14:50:47 -0500 Message-ID: <17636.1295639447@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-1.91 tagged_above=-10 required=5 tests=BAYES_00=-1.9, T_RP_MATCHES_RCVD=-0.01 X-Spam-Level: X-Archive-Number: 201101/203 X-Sequence-Number: 41990 grant@amadensor.com writes: > Here is the fun part. When running 8 threads spinning calculating square > roots (using the stress package), the full scan returned consistently 60% > faster than the machine with no load. Possibly the synchronized-seqscans logic kicking in, resulting in this guy not having to do all his own I/Os. It would be difficult to make any trustworthy conclusions about performance in such cases from a view of only one process's results --- you'd need to look at the aggregate behavior to understand what's happening. regards, tom lane