Received: from maia.hub.org (maia-3.hub.org [200.46.204.243]) by mail.postgresql.org (Postfix) with ESMTP id 10E8B1337B68 for ; Tue, 26 Apr 2011 02:34:59 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.204.243]) (amavisd-maia, port 10024) with ESMTP id 92956-01 for ; Tue, 26 Apr 2011 05:34:51 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-qy0-f181.google.com (mail-qy0-f181.google.com [209.85.216.181]) by mail.postgresql.org (Postfix) with ESMTP id DE8331337A5D for ; Tue, 26 Apr 2011 02:34:50 -0300 (ADT) Received: by qyg14 with SMTP id 14so132795qyg.19 for ; Mon, 25 Apr 2011 22:34:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:references:in-reply-to:mime-version :content-transfer-encoding:content-type:message-id:cc:x-mailer:from :subject:date:to; bh=Xfss86U5PfSRwAWkokITd0CLR78kZ/eYWZgeOHbisAs=; b=aW2IS85SjC0z6HPjEP9uFMQXTZme+eGGINHIerShjDkVQlX1qAwbJQsg0Ul+5seolB TpXpz5aRRwiTjdP3cV7nv9zHK3FIzj8hVY7DPVuNwTGgXR+0/g/KkQQVPcV3Ui8hrKVU NtzbVhmhQMona1XpZGnW+3+HNb3fTYjY0RWKk= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=references:in-reply-to:mime-version:content-transfer-encoding :content-type:message-id:cc:x-mailer:from:subject:date:to; b=LV1A8z8/2c6JACHXJ6TO4QxYiX3H21HkslCw51kMZqOwKT/fu47VMB1Nw7EKkO5BAD 6LmZzt7OwNJ5kyJa2CAk8EPYbduMA0gVHk6taAjpyYjyUpNE31v69Wh8osR2F/VPdfpm 2qaGmF/npOp34ch3WSNbfVG9Y0Fx1f7eesnvU= Received: by 10.229.100.215 with SMTP id z23mr221235qcn.294.1303796090492; Mon, 25 Apr 2011 22:34:50 -0700 (PDT) Received: from [192.168.2.5] (pool-71-188-33-7.cmdnnj.east.verizon.net [71.188.33.7]) by mx.google.com with ESMTPS id f5sm4581804qck.20.2011.04.25.22.34.49 (version=TLSv1/SSLv3 cipher=OTHER); Mon, 25 Apr 2011 22:34:49 -0700 (PDT) References: <20110412171855.GA14292@tux> <4DA496FA.3070908@fuzzy.cz> <8F22D592-23C1-4A3C-94A5-48363332ADD3@darkstatic.com> <4DA4BFA2.5060601@fuzzy.cz> <4DA4D40A.4010200@fuzzy.cz> <4DA56DA8020000250003C783@gw.wicourts.gov> <4DA6216E.9020907@fuzzy.cz> In-Reply-To: <4DA6216E.9020907@fuzzy.cz> Mime-Version: 1.0 (iPhone Mail 8A293) Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii Message-Id: <11589CE9-B860-4024-BCDF-88FBE00FB9BC@gmail.com> Cc: "pgsql-performance@postgresql.org" X-Mailer: iPhone Mail (8A293) From: Robert Haas Subject: Re: Performance Date: Tue, 26 Apr 2011 01:35:35 -0400 To: Tomas Vondra X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-1.897 tagged_above=-10 required=5 tests=BAYES_00=-1.9, FREEMAIL_FROM=0.001, MIME_QP_LONG_LINE=0.001, RFC_ABUSE_POST=0.001 X-Spam-Level: X-Archive-Number: 201104/349 X-Sequence-Number: 43411 On Apr 13, 2011, at 6:19 PM, Tomas Vondra wrote: > Yes, I've had some lectures on non-linear programming so I'm aware that > this won't work if the cost function has multiple extremes (walleys / > hills etc.) but I somehow suppose that's not the case of cost estimates. I think that supposition might turn out to be incorrect, though. Probably w= hat will happen on simple queries is that a small change will make no differ= ence, and a large enough change will cause a plan change. On complex querie= s it will approach continuous variation but why shouldn't there be local min= ima? ...Robert=