Re: gaussian distribution pgbench

From: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
To: Mitsumasa KONDO <kondo(dot)mitsumasa(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: gaussian distribution pgbench
Date: 2014-07-18 12:29:03
Message-ID: alpine.DEB.2.10.1407181418330.15105@sto
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> For example, when we set the number of transaction 10,000 (-t 10000),
> range of aid is 100,000,
> and --exponential is 10, decile percents is under following as you know.
>
> decile percents: 63.2% 23.3% 8.6% 3.1% 1.2% 0.4% 0.2% 0.1% 0.0% 0.0%
> highest/lowest percent of the range: 9.5% 0.0%
>
> They mean that,
> #number of access in range of aid (from decile percents):
> 1 to 10,000 => 6,320 times
> 10,001 to 20,000 => 2,330 times
> 20,001 to 30,000 => 860 times
> ...
> 90,001 to 10,0000 => 0 times
>
> #number of access in range of aid (from highest/lowest percent of the
> range):
> 1 to 1,000 => 950 times
> ...
> 99,001 to 10,0000 => 0 times
>
> that's all.
>
> Their information is easy to understand distribution of access probability,
> isn't it?
> Maybe I and Fabien-san have a knowledge of mathematics, so we think decile
> percentage is common sense.
> But if it isn't common sense, I agree with adding about these explanation
> in the documents.

What we are talking about is the "summary" at the end of the run, which is
expected to be compact, hence the terse few lines.

I'm not sure how to make it explicit without extending the summary too
much, so it would not be a summary anymore:-)

My initial assumption is that anyone interested enough in changing the
default uniform distribution for a test would know about decile, but that
seems to be optimistic.

Maybe it would be okay to keep a terse summary but to expand the
documentation to explain what it means, as you suggested above...

--
Fabien.

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