Received: from localhost (maia-2.hub.org [200.46.204.187]) by postgresql.org (Postfix) with ESMTP id D27619FA0EE; Tue, 19 Dec 2006 00:43:20 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.187]) (amavisd-new, port 10024) with ESMTP id 11655-03; Tue, 19 Dec 2006 00:43:15 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey-1.7.4 X-Greylist: from auto-whitelisted by SQLgrey-1.7.4 Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by postgresql.org (Postfix) with ESMTP id 20DAB9F9398; Tue, 19 Dec 2006 00:43:16 -0400 (AST) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.13.6/8.13.6) with ESMTP id kBJ4h1Dj010652; Mon, 18 Dec 2006 23:43:01 -0500 (EST) To: "Simon Riggs" cc: "Peter Eisentraut" , pgsql-hackers@postgresql.org, "Kelly Burkhart" , "Evgeny Gridasov" , pgsql-performance@postgresql.org Subject: Re: [HACKERS] EXPLAIN ANALYZE on 8.2 In-reply-to: <1166481204.3654.174.camel@silverbirch.site> References: <20061214163230.d46f0138.eugrid@fpm.kubsu.ru> <29450.1166141131@sss.pgh.pa.us> <1166178488.3882.56.camel@silverbirch.site> <200612151406.57851.peter_e@gmx.net> <9227.1166198245@sss.pgh.pa.us> <1166481204.3654.174.camel@silverbirch.site> Comments: In-reply-to "Simon Riggs" message dated "Mon, 18 Dec 2006 22:33:23 +0000" Date: Mon, 18 Dec 2006 23:43:00 -0500 Message-ID: <10651.1166503380@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200612/471 X-Sequence-Number: 22527 "Simon Riggs" writes: > On Fri, 2006-12-15 at 09:56 -0500, Tom Lane wrote: >> The fundamental problem with it was the assumption that different >> executions of a plan node will have the same timing. That's not true, >> in fact not even approximately true. > It doesn't make sense to me to claim that the timing is so important > that we cannot do without it, at the same time as saying it isn't even > approximately true that is highly variable. Huh? What I said was that successive executions of the same plan node may take considerably different amounts of time, and the proposed sampling patch failed to handle that situation with acceptable accuracy. regards, tom lane