From: | Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> |
---|---|
To: | Ildar Musin <i(dot)musin(at)postgrespro(dot)ru> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: General purpose hashing func in pgbench |
Date: | 2018-01-12 15:03:59 |
Message-ID: | alpine.DEB.2.20.1801121603110.13422@lancre |
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Thread: | |
Lists: | pgsql-hackers |
>> 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.
Yes, exactly. What is desirable may depend on the use case, though.
--
Fabien.
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