Received: from malur.postgresql.org ([217.196.149.56]) by arkaria.postgresql.org with esmtp (Exim 4.80) (envelope-from ) id 1Ynw3q-0001xj-8k for pgsql-hackers@arkaria.postgresql.org; Thu, 30 Apr 2015 21:31:58 +0000 Received: from localhost ([127.0.0.1] helo=postgresql.org) by malur.postgresql.org with smtp (Exim 4.80) (envelope-from ) id 1Ynw3p-0000E0-Oj for pgsql-hackers@arkaria.postgresql.org; Thu, 30 Apr 2015 21:31:57 +0000 Received: from makus.postgresql.org ([2001:4800:1501:1::229]) by malur.postgresql.org with esmtps (TLS1.2:RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1Ynw3n-0000Dt-QE for pgsql-hackers@postgresql.org; Thu, 30 Apr 2015 21:31:56 +0000 Received: from mail-pd0-x231.google.com ([2607:f8b0:400e:c02::231]) by makus.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.84) (envelope-from ) id 1Ynw3k-0000Bo-Un for pgsql-hackers@postgresql.org; Thu, 30 Apr 2015 21:31:54 +0000 Received: by pdbqd1 with SMTP id qd1so72824781pdb.2 for ; Thu, 30 Apr 2015 14:31:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:message-id:date:from:reply-to:user-agent:mime-version:to:cc :subject:references:in-reply-to:content-type :content-transfer-encoding; bh=GwNXsMJpbFMseM8E58Dv4ZJnJThEBTFCGQqVUzGgC84=; b=FUELQqbaIZZN1xub/HCc79cUNOs/GL2P4qEux/YIcePSgaDu6xfHpK5e/+WLhsvid2 wgIL8q/iPnY49/6d0a17QjOew9v+2RXfV7xhuDJlI774IcWBi+ETfO+p+GihlmTaL2uF yXs8P2f5dFfeh69WcsZxhq9gOQJAdkU2+HGltQ19REf/CK10MFt5yUzK+UaMD1SLYsbh 6c0z0CSZ5N17NJZ39sghD8gAmlykCr4FctRwocg0sLyo2Oxc5Wi2M6j++ItZuG1RCtT+ SMrG6aDtC3ydyMlBrMyUaYfjrkemXJgVLyKOWCAGs2WFvYOi1GRmGuG+YngezMz8VY4Z vVug== X-Received: by 10.70.109.131 with SMTP id hs3mr12033907pdb.40.1430429511446; Thu, 30 Apr 2015 14:31:51 -0700 (PDT) Received: from [192.168.96.239] (50-204-244-30-static.hfc.comcastbusiness.net. [50.204.244.30]) by mx.google.com with ESMTPSA id dv3sm3035428pbb.91.2015.04.30.14.31.50 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 30 Apr 2015 14:31:50 -0700 (PDT) Message-ID: <55429F44.2070205@iki.fi> Date: Thu, 30 Apr 2015 14:31:48 -0700 From: Heikki Linnakangas Reply-To: hlinnaka@iki.fi User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.6.0 MIME-Version: 1.0 To: Robert Haas , Tomas Vondra CC: "pgsql-hackers@postgresql.org" Subject: Re: PATCH: adaptive ndistinct estimator v4 References: <541A2335.3060100@agliodbs.com> <542C4E60.3030505@agliodbs.com> <542DADEB.2080103@agliodbs.com> <54381D20.9010501@fuzzy.cz> <5472416C.3080506@fuzzy.cz> <5483B346.6000203@fuzzy.cz> <551AEF45.7010700@2ndquadrant.com> In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Pg-Spam-Score: -2.4 (--) List-Archive: List-Help: List-ID: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: X-Mailing-List: pgsql-hackers Precedence: bulk Sender: pgsql-hackers-owner@postgresql.org On 04/30/2015 01:57 PM, Robert Haas wrote: > > 2. There should be a compatibility GUC to restore the old behavior. > The new behavior should be the default, because if we're not confident > that the new behavior will be better for most people, we have no > business installing it in the first place (plus few people will try > it). But just in case it turns out to suck for some people, we should > provide an escape hatch, at least for a few releases. You can override the ndistinct estimate with ALTER TABLE. I think that's enough for an escape hatch. - Heikki -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers