From: =?iso-8859-15?q?C=E9dric_Villemain?= <cedric@2ndquadrant.com>
Reply-To: cedric@2ndquadrant.com
Organization: 2ndQuadrant
To: pgsql-performance@postgresql.org
Subject: Re: Hints (was Poor performance using CTE)
Date: Fri, 23 Nov 2012 11:05:52 +0100
User-Agent: KMail/1.13.7 (Linux/3.2.0-4-amd64; KDE/4.8.4; x86_64; ; )
Cc: Craig James <cjames@emolecules.com>, Kevin Grittner <kgrittn@mail.com>,
	Craig Ringer <craig@2ndquadrant.com>, Tom Lane <tgl@sss.pgh.pa.us>,
	Claudio Freire <klaussfreire@gmail.com>,
	Merlin Moncure <mmoncure@gmail.com>,
	David Greco <David_Greco@harte-hanks.com>
References: <20121121134232.68590@gmx.com>
	<CAFwQ8reE2vLynnE9zO_i7WhmktbiKaSYbBrCvJXCQ62feqBGZQ@mail.gmail.com>
In-Reply-To: 
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Le mercredi 21 novembre 2012 17:34:02, Craig James a =E9crit :
> On Wed, Nov 21, 2012 at 5:42 AM, Kevin Grittner <kgrittn@mail.com> wrote:
> > It's a tough problem. Disguising and not documenting the available
> > optimizer hints leads to more reports on where the optimizer should
> > be smarter, and has spurred optimizer improvements. ...
> > Regarding the above-mentioned benefits we would stand to lose by
> > having clear and documented hints, perhaps we could occasionally
> > solicit input on where people are finding hints useful to get ideas
> > on where we might want to improve the optimizer. As far as worrying
> > about people using hints to force a plan which is sub-optimal --
> > isn't that getting into nanny mode a bit too much?
>=20
> Toward that end, the hint documentation (which is almost always viewed as
> HTML) could be prefaced by a strong suggestion to post performance
> questions in this group first, with links to the "subscribe" page and the
> "how to report performance problems" FAQ. The hint documentation could ev=
en
> be minimalistic; suggest to developers that they should post their
> problematic queries here before resorting to hints.  That would give the
> experts an opportunity to provide the normal advice.  The correct hint
> syntax would be suggested only when all other avenues failed.

We have hooks in PostgreSQL. We already have at least one extension which i=
s=20
using that to change the planner behavior.

We can have a bit more hooks and try to improve the cost estimate, this par=
t=20
of the code is known to be built by reports and human estimations, also the=
=20
9.2 version got heavy modifications in this area.=20

Let the 'Hints' be inside an extension thus we are able to track them and f=
ix=20
the planner/costestimate issues.

I don't see why PostgreSQL needs 'Hints' *in-core*.
=2D-=20
C=E9dric Villemain +33 (0)6 20 30 22 52
http://2ndQuadrant.fr/
PostgreSQL: Support 24x7 - D=E9veloppement, Expertise et Formation

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