Subject: Re: General purpose hashing func in pgbench
To: Fabien COELHO <coelho@cri.ensmp.fr>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
References: <0e8bd39e-dfcd-2879-f88f-272799ad7ef2@postgrespro.ru>
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From: Ildar Musin <i.musin@postgrespro.ru>
Message-ID: <9603bac9-ae5d-36c5-5978-a88bdb700e37@postgrespro.ru>
Date: Tue, 9 Jan 2018 19:22:14 +0300
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Hello Fabien,


25/12/2017 19:17, Fabien COELHO пишет:
>
>>> However, the key can be used if controlled so that different values do
>>> not have the same randomization in different part of the script, so as
>>> to avoid using the same patterns for different things if not desirable.
>>
>> Original murmur algorithm accepts seed as a parameter, which can be used
>> for this purpose. I used value itself as a seed in the patch, but I can
>> turn it into a function argument.
>
> Hmmm. Possibly. However it needs a default, something like
>
>   x = hash(v[, key])
>
> with key some pseudo-random value?
>
Sorry for a long delay. I've added hash() function which is just an
alias for murmur2. I've also utilized variable arguments feature from
least()/greates() functions to make optional seed parameter, but I
consider this as a hack. Should we probably add some infrastructure for
optional arguments? Docs and tests are on their way.

Thanks!

-- 
Ildar Musin
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company 


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