To: Stefan Kaltenbrunner <stefan@kaltenbrunner.cc>
cc: Julius Stroffek <Julius.Stroffek@Sun.COM>,
	pgsql-performance@postgresql.org, pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Proposal: Pluggable Optimizer Interface 
In-reply-to: <46C0BD13.107@kaltenbrunner.cc> 
References: <46C0B5E4.4020305@sun.com> <46C0BD13.107@kaltenbrunner.cc>
Comments: In-reply-to Stefan Kaltenbrunner <stefan@kaltenbrunner.cc>
	message dated "Mon, 13 Aug 2007 22:20:35 +0200"
Date: Mon, 13 Aug 2007 17:23:23 -0400
Message-ID: <22245.1187040203@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Stefan Kaltenbrunner <stefan@kaltenbrunner.cc> writes:
> Julius Stroffek wrote:
>> There is a proposal attached to this mail about the interface
>> we would like to implement for switching between different
>> optimizers. Please review it and provide a feedback to us.

> hmm - how does is that proposal different from what got implemented with:
> http://archives.postgresql.org/pgsql-committers/2007-05/msg00315.php

Well, it's a very different level of abstraction.  The planner_hook
would allow you to replace the *entire* planner, but if you only want to
replace GEQO (that is, only substitute some other heuristics for partial
search of a large join-order space), doing it from planner_hook will
probably require duplicating a great deal of code.  A hook right at the
place where we currently choose "geqo or regular" would be a lot easier
to experiment with.

Replacing GEQO sounds like a fine area for investigation to me; I've
always been dubious about whether it's doing a good job.  But I'd prefer
a simple hook function pointer designed in the same style as
planner_hook (ie, intended to be overridden by a loadable module).
The proposed addition of a system catalog and SQL-level management
commands sounds like a great way to waste a lot of effort on mere
decoration, before ever getting to the point of being able to
demonstrate that there's any value in it.  Also, while we might accept
a small hook-function patch for 8.3, there's zero chance of any of that
other stuff making it into this release cycle.

			regards, tom lane