From: Andres Freund <andres@anarazel.de>
To: Andrew Dunstan <andrew@dunslane.net>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Heikki Linnakangas <hlinnakangas@vmware.com>
Cc: Craig Ringer <craig@2ndQuadrant.com>
Cc: Claudio Freire <klaussfreire@gmail.com>
Cc: Merlin Moncure <mmoncure@gmail.com>
Cc: David Greco <David_Greco@harte-hanks.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Poor performance using CTE
Date: Wed, 21 Nov 2012 16:32:09 +0100
Message-ID: <20121121153209.GA1271@awork2.anarazel.de> (raw)
In-Reply-To: <50ACF16C.2020902@dunslane.net>
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<50AC1472.3050607@2ndQuadrant.com>
<18123.1353455585@sss.pgh.pa.us>
<50ACD166.1000507@vmware.com>
<50ACE970.7050701@dunslane.net>
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<50ACF16C.2020902@dunslane.net>
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
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To: pgsql-performance@postgresql.org
Cc: andres@anarazel.de, andrew@dunslane.net, tgl@sss.pgh.pa.us, hlinnakangas@vmware.com, craig@2ndQuadrant.com, klaussfreire@gmail.com, mmoncure@gmail.com, David_Greco@harte-hanks.com
Subject: Re: Poor performance using CTE
In-Reply-To: <20121121153209.GA1271@awork2.anarazel.de>
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