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From: Shaun Thomas <sthomas@peak6.com>
To: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: Josh Berkus <josh@agliodbs.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Why we don't want hints Was: Slow count(*)	 again...
Date: Thu, 10 Feb 2011 11:06:42 -0600
Message-ID: <4D541B22.9080000@peak6.com> (raw)
In-Reply-To: <4D53C1C0020000250003A783@gw.wicourts.gov>
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On 02/10/2011 10:45 AM, Kevin Grittner wrote:

> Even there I would tend to think that the sort of "do it this way"
> hints that people seem to initially want wouldn't be good; it should
> be a way to override the costing factor which the optimizer gets
> wrong, so it can do its usual excellent job of evaluating plans with
> accurate costs.

You know... that's an interesting approach. We already do that with 
functions by allowing users to specify the estimated cost, rows 
returned, and even override config settings. It's an inexact science at 
best, but it might help the optimizer out.

Really... how difficult would it be to add that syntax to the JOIN 
statement, for example?

-- 
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd. | Suite 800 | Chicago IL, 60604
312-676-8870
sthomas@peak6.com

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