From: | Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> |
---|---|
To: | Alik Khilazhev <a(dot)khilazhev(at)postgrespro(dot)ru> |
Cc: | PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [WIP] Zipfian distribution in pgbench |
Date: | 2017-07-17 11:42:13 |
Message-ID: | alpine.DEB.2.20.1707171335210.9472@lancre |
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Thread: | |
Lists: | pgsql-hackers |
Hello,
>> Is this bias expected from the drawing method, say because it is
>> approximated and the approximation is weak at some points, or is there
>> an issue with its implementation, says some shift which gets smoothed
>> down for higher indexes?
>
> I have checked paper where such implementation was proposed and there
> theta allowed only on range between 0 and 1. It seems like it is not
> guaranteed that it should work well when theta is more than 1.
Ok.
I see a significant issue with having a random_zipfian function which does
not really return a zipfian distribution under some parameter values. If
there is no better alternative, I would suggest to restrict the parameter
for values between 0 and 1, or to find a better approximation for theta >=
0.
> I am attaching paper, see page 23.
Thanks for the paper. It reminds me that I intended to propose a
parametric pseudo-random permutation for pgbench, some day.
--
Fabien.
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