Received: from malur.postgresql.org ([217.196.149.56])
	by arkaria.postgresql.org with esmtp (Exim 4.72) (envelope-from
	<pgsql-performance-owner+M49732=pgsql-performance-ar@postgresql.org>)
	id 1USq3a-00032H-JT for pgsql-performance@arkaria.postgresql.org;
	Thu, 18 Apr 2013 14:43:26 +0000
Received: from localhost ([127.0.0.1] helo=postgresql.org)
	by malur.postgresql.org with smtp (Exim 4.72) (envelope-from
	<pgsql-performance-owner+M49732=pgsql-performance-ar@postgresql.org>)
	id 1USq3a-0008Pj-48 for pgsql-performance@arkaria.postgresql.org;
	Thu, 18 Apr 2013 14:43:26 +0000
Received: from magus.postgresql.org ([2a02:c0:301:0:ffff::29])
	by malur.postgresql.org with esmtp (Exim 4.72)
	(envelope-from <dev@archonet.com>) id 1USq3Z-0008Pe-Df
	for pgsql-performance@postgresql.org; Thu, 18 Apr 2013 14:43:25 +0000
Received: from archon2012.plus.com ([80.229.41.160] helo=mail.archonet.com)
	by magus.postgresql.org with esmtp (Exim 4.72)
	(envelope-from <dev@archonet.com>) id 1USq3W-0003AU-Gh
	for pgsql-performance@postgresql.org; Thu, 18 Apr 2013 14:43:25 +0000
Received: from [192.168.1.13] (ariel.office.archonet.com [192.168.1.13])
	by mail.archonet.com (Postfix) with ESMTP id 8C45E2C0268;
	Thu, 18 Apr 2013 15:43:20 +0100 (BST)
Message-ID: <51700688.4050505@archonet.com>
Date: Thu, 18 Apr 2013 15:43:20 +0100
From: Richard Huxton <dev@archonet.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64;
	rv:10.0.12) Gecko/20130116 Icedove/10.0.12
MIME-Version: 1.0
To: dmitry potapov <potapov.dmitry@gmail.com>
CC: pgsql-performance@postgresql.org
Subject: Re: "WHERE 1 = 2 OR ..." makes planner choose a very inefficient plan
References: 
 <CAJPZb_vmf3dkCv0Rre+VOm6bkJc3hugjEE2h0bgY1WqduDLUbg@mail.gmail.com>
In-Reply-To: 
 <CAJPZb_vmf3dkCv0Rre+VOm6bkJc3hugjEE2h0bgY1WqduDLUbg@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Pg-Spam-Score: -1.9 (-)
List-Archive: <http://archives.postgresql.org/pgsql-performance>
List-Help: <mailto:majordomo@postgresql.org?body=help>
List-ID: <pgsql-performance.postgresql.org>
List-Owner: <mailto:pgsql-performance-owner@postgresql.org>
List-Post: <mailto:pgsql-performance@postgresql.org>
List-Subscribe: <mailto:majordomo@postgresql.org?body=sub%20pgsql-performance>
List-Unsubscribe: 
 <mailto:majordomo@postgresql.org?body=unsub%20pgsql-performance>
X-Mailing-List: pgsql-performance
Precedence: bulk
Sender: pgsql-performance-owner@postgresql.org

On 18/04/13 15:20, dmitry potapov wrote:
> Hello,
>
> I recently stumbled upon on what could be a planner bug or a corner
> case. If "<false condition> OR ..." is added to WHERE clause of SELECT
> query, then the planner chooses a very inefficient plan. Consider a query:

> If I comment out "1=2 OR", then the plan changes dramatically:

What happens if you substitute:
1. 1=3   OR
2. false OR

-- 
   Richard Huxton
   Archonet Ltd


-- 
Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-performance