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From: Andres Freund <andres@2ndquadrant.com>
To: Claudio Freire <klaussfreire@gmail.com>
Cc: 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: 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 17:24:16 +0100
Message-ID: <20121121162416.GA6268@awork2.anarazel.de> (raw)
In-Reply-To: <CAGTBQpa14GQ+L9KSKdS+kXVWYkoEVNUBbvaUpgRjskufEx-=-A@mail.gmail.com>
References: <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>
	<CAGTBQpa14GQ+L9KSKdS+kXVWYkoEVNUBbvaUpgRjskufEx-=-A@mail.gmail.com>

On 2012-11-21 13:16:25 -0300, Claudio Freire wrote:
> On Wed, Nov 21, 2012 at 12:32 PM, Andres Freund <andres@anarazel.de> wrote:
> > +1
> >
> > WITH foo AS (SELECT ...) (barrier=on|off)?
> >
> > 9.3 introduces the syntax, defaulting to on
> > 9.4 switches the default to off.
>
> Why syntax? What about a guc?
>
> collapse_cte_limit?

Because there are very good reasons to want to current behaviour. A guc
is a global either/or so I don't see it helping much.

Greetings,

Andres Freund

--
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services




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