Re: General purpose hashing func in pgbench

From: Ildar Musin <i(dot)musin(at)postgrespro(dot)ru>
To: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: General purpose hashing func in pgbench
Date: 2018-01-11 16:21:46
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10/01/2018 21:42, Fabien COELHO пишет:
> Hmm. I do not think that we should want a shared seed value. The seed
> should be different for each call so as to avoid undesired
> correlations. If wanted, correlation could be obtained by using an
> explicit identical seed.
> ISTM that the best way to add the seed is to call random() when the
> second arg is missing in make_func. Also, this means that the executor
> would always get its two arguments, so it would simplify the code there.
Ok, I think I understand what you meant. You meant the case like following:

\set x random(1, 100)
\set h1 hash(:x)
\set h2 hash(:x)  -- will have different seed from h1

so that different instances of hash function within one script would
have different seeds. Yes, that is a good idea, I can do that.

Ildar Musin
Postgres Professional:
Russian Postgres Company

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