Re: [WIP] Zipfian distribution in pgbench

From: Alik Khilazhev <a(dot)khilazhev(at)postgrespro(dot)ru>
To: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
Cc: PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [WIP] Zipfian distribution in pgbench
Date: 2017-08-06 18:22:26
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Hello Fabien,

> On 5 Aug 2017, at 12:15, Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> wrote:
> Hello Alik,
> I've done some math investigations, which consisted in spending one hour with Christian, a statistician colleague of mine. He took an old book out of a shelf, opened it to page 550 (roughly in the middle), and explained to me how to build a real zipfian distribution random generator.
> The iterative method is for parameter a>1 and works for unbounded values. It is simple to add a bound. In practice the iterative method is quite effective, i.e. number of iterations is typically small, at least if the bound is large and if parameter a is not too close to 1.

> I've attached a python3 script which implements the algorithm. It looks like magic. Beware that a C implementation should take care of float and int overflows.
Thank you for the script. I will rewrite it to C and add to the patch soon.

Thanks and Regards,
Alik Khilazhev
Postgres Professional:
The Russian Postgres Company

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