Message-ID: <50ACF658.10902@archidevsys.co.nz>
Date: Thu, 22 Nov 2012 04:42:16 +1300
From: Gavin Flower <GavinFlower@archidevsys.co.nz>
Organization: ArchiDevSys
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To: Andres Freund <andres@anarazel.de>
CC: Andrew Dunstan <andrew@dunslane.net>, Tom Lane <tgl@sss.pgh.pa.us>,
	Heikki Linnakangas <hlinnakangas@vmware.com>,
	Craig Ringer <craig@2ndQuadrant.com>,
	Claudio Freire <klaussfreire@gmail.com>,
	Merlin Moncure <mmoncure@gmail.com>,
	David Greco <David_Greco@harte-hanks.com>,
	"pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Subject: Re: Poor performance using CTE
References: 
 <CAHyXU0xeEVX2P=HaNxPiKayEhkWp3GobgAXCQPrfsqbawXVV-w@mail.gmail.com>
	<CAGTBQpZ_Za-XSXvmPUx3F7wgeX=HB1xUpDsn+1DXY3a87YJLBQ@mail.gmail.com>
	<CAHyXU0z4oUss50vhH_wGZ-HERQe9wCMSf1nMTGNddXeCoKvVVA@mail.gmail.com>
	<CAGTBQpbf9bdJ3gjcYdw2FuPmN=dqx+wE7opsCp515cEndpGDYw@mail.gmail.com>
	<50AC1472.3050607@2ndQuadrant.com>
	<18123.1353455585@sss.pgh.pa.us> <50ACD166.1000507@vmware.com>
	<50ACE970.7050701@dunslane.net> <3396.1353509947@sss.pgh.pa.us>
	<50ACF16C.2020902@dunslane.net>
	<20121121153209.GA1271@awork2.anarazel.de>
In-Reply-To: <20121121153209.GA1271@awork2.anarazel.de>
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On 22/11/12 04:32, Andres Freund wrote:
> On 2012-11-21 10:21:16 -0500, Andrew Dunstan wrote:
>> On 11/21/2012 09:59 AM, Tom Lane wrote:
>>> Andrew Dunstan <andrew@dunslane.net> writes:
>>>> If we're going to do it can we please come up with something more
>>>> intuitive and much, much more documented than "OFFSET 0"? And if/when we
>>>> do this we'll need to have big red warnings all over then release notes,
>>>> since a lot of people I know will need to do some extensive remediation
>>>> before moving to such a release.
>>> The probability that we would actually *remove* that behavior of OFFSET
>>> 0 is not distinguishable from zero.  I'm not terribly excited about
>>> having an alternate syntax to specify an optimization fence, but even
>>> if we do create such a thing, there's no need to break the historical
>>> usage.
>>>
>> I wasn't talking about removing it. My point was that if the optimization
>> fence around CTEs is removed a lot of people will need to rework apps where
>> they have used them for that purpose. And I continue to think that spelling
>> it "OFFSET 0" is horribly obscure.
> +1
>
> WITH foo AS (SELECT ...) (barrier=on|off)?
>
> 9.3 introduces the syntax, defaulting to on
> 9.4 switches the default to off.
>
> Greetings,
>
> Andres Freund
>
>

WITH foo AS (SELECT ...) (fence=on|off)?


WITH foo AS (SELECT ...) (optimisation_fence=on|off)?