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From: Robert Haas <robertmhaas@gmail.com>
To: Tomas Vondra <tv@fuzzy.cz>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Performance
Date: Tue, 26 Apr 2011 01:35:35 -0400
Message-ID: <11589CE9-B860-4024-BCDF-88FBE00FB9BC@gmail.com> (raw)
In-Reply-To: <4DA6216E.9020907@fuzzy.cz>
References: <DF2D5436-117C-4D02-9B3C-A55723B7DDE1@darkstatic.com>
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	<4DA496FA.3070908@fuzzy.cz>
	<8F22D592-23C1-4A3C-94A5-48363332ADD3@darkstatic.com>
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	<4DA56DA8020000250003C783@gw.wicourts.gov>
	<BANLkTinJqXqErAtQg--1MOaw2LJNFZmwOg@mail.gmail.com>
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	<4DA6216E.9020907@fuzzy.cz>

On Apr 13, 2011, at 6:19 PM, Tomas Vondra <tv@fuzzy.cz> wrote:
> Yes, I've had some lectures on non-linear programming so I'm aware that
> this won't work if the cost function has multiple extremes (walleys /
> hills etc.) but I somehow suppose that's not the case of cost estimates.

I think that supposition might turn out to be incorrect, though.  Probably what will happen on simple queries is that a small change will make no difference, and a large enough change will cause a plan change.  On complex queries it will approach continuous variation but why shouldn't there be local minima?

...Robert


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