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From: Jesper Krogh <jesper@krogh.cc>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-performance@postgresql.org
Subject: Re: planner costs in "warm cache" tests
Date: Mon, 31 May 2010 20:48:40 +0200
Message-ID: <4C040488.30906@krogh.cc> (raw)
In-Reply-To: <14644.1275244491@sss.pgh.pa.us>
References: <4C02A342.40801@krogh.cc>
<14644.1275244491@sss.pgh.pa.us>
On 2010-05-30 20:34, Tom Lane wrote:
> Jesper Krogh<jesper@krogh.cc> writes:
>
>> testdb=# set seq_page_cost = 0.00001;
>> SET
>> testdb=# set random_page_cost = 0.00001;
>> SET
>>
> Well, hmm, I really doubt that that represents reality either. A page
> access is by no means "free" even when the page is already in cache.
> I don't recall anyone suggesting that you set these numbers to less
> than perhaps 0.01.
>
>
Thank you for the prompt response. Is it a "false assumption" that the
cost should in some metric between different plans be a measurement
of actual run-time in a dead-disk run?
It should most likely be matching a typical workload situation, but that
it really hard to tell anything about, so my "feeling" would be that the
dead disk case is the one closest?
--
Jesper
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