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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Claudio Freire <klaussfreire@gmail.com>
Cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: Ogden <lists@darkstatic.com>
Cc: Tomas Vondra <tv@fuzzy.cz>
Cc: pgsql-performance@postgresql.org
Subject: Re: Performance
Date: Wed, 13 Apr 2011 17:52:36 -0400
Message-ID: <25734.1302731556@sss.pgh.pa.us> (raw)
In-Reply-To: <BANLkTinJqXqErAtQg--1MOaw2LJNFZmwOg@mail.gmail.com>
References: <DF2D5436-117C-4D02-9B3C-A55723B7DDE1@darkstatic.com>
	<20110412171855.GA14292@tux>
	<FC3A3A2B-3ECB-41BA-8F94-356D6FED3695@darkstatic.com>
	<4DA496FA.3070908@fuzzy.cz>
	<8F22D592-23C1-4A3C-94A5-48363332ADD3@darkstatic.com>
	<4DA4BFA2.5060601@fuzzy.cz>
	<B93DFBBB-DA56-4044-A508-0B7E4A2CFD28@darkstatic.com>
	<4DA4D40A.4010200@fuzzy.cz>
	<A0B9339E-9D58-4842-A206-050B773360B6@darkstatic.com>
	<4DA56DA8020000250003C783@gw.wicourts.gov>
	<BANLkTinJqXqErAtQg--1MOaw2LJNFZmwOg@mail.gmail.com>

Claudio Freire <klaussfreire@gmail.com> writes:
> On Wed, Apr 13, 2011 at 4:32 PM, Kevin Grittner
> <Kevin.Grittner@wicourts.gov> wrote:
>> If you model the costing to reflect the reality on your server, good
>> plans will be chosen.

> Wouldn't it be "better" to derive those costs from actual performance
> data measured at runtime?

> Say, pg could measure random/seq page cost, *per tablespace* even.

> Has that been tried?

Getting numbers that mean much of anything is a slow, expensive
process.  You really don't want the database trying to do that for you.
Once you've got them, you *really* don't want the database
editorializing on them.

			regards, tom lane



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