pg.ddx.io  pgsql-performance@postgresql.org mailing list archive  

help / color / mirror / Atom feed
From: Craig Ringer <craig@2ndQuadrant.com>
To: Gavin Flower <GavinFlower@archidevsys.co.nz>
Cc: Heikki Linnakangas <hlinnakangas@vmware.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: Andrew Dunstan <andrew@dunslane.net>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
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: Thu, 22 Nov 2012 08:42:51 +0800
Message-ID: <50AD750B.8010108@2ndQuadrant.com> (raw)
In-Reply-To: <50AD741E.1060100@archidevsys.co.nz>
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>
	<50ACF658.10902@archidevsys.co.nz>
	<50ACF991.3020603@vmware.com>
	<50AD2BD1.8070206@archidevsys.co.nz>
	<50AD6D16.9040608@2ndQuadrant.com>
	<50AD741E.1060100@archidevsys.co.nz>

On 11/22/2012 08:38 AM, Gavin Flower wrote:
> I suspect most people are blissfully unaware of CTE's being fenced, or
> at least not really sure what it means. So I suspect NOT FENCE would
> be the better default.
It's also probably more standard, and a better fit with what other DBs do.

Pg would still need to detect conditions like the use of functions with
side effects or (obviously) INSERT/UPDATE/DELETE wCTEs and not push
conditions down into them / pull conditions up from them, etc. That's
how I read the standard, though; must have the same effect as if the
queries were executed as written, so Pg is free to transform them so
long as it doesn't change the results.

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





view thread (36+ messages)  latest in thread

Message-ID: <50AD750B.8010108@2ndQuadrant.com>
Permalink:  ../50AD750B.8010108@2ndQuadrant.com/
Also on:    postgresql.org/message-id/50AD750B.8010108@2ndQuadrant.com

 · 

reply
Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: pgsql-performance@postgresql.org
  Cc: craig@2ndQuadrant.com, GavinFlower@archidevsys.co.nz, hlinnakangas@vmware.com, andres@anarazel.de, andrew@dunslane.net, tgl@sss.pgh.pa.us, klaussfreire@gmail.com, mmoncure@gmail.com, David_Greco@harte-hanks.com
  Subject: Re: Poor performance using CTE
  In-Reply-To: <50AD750B.8010108@2ndQuadrant.com>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox