|From:||"Daniel Verite" <daniel(at)manitou-mail(dot)org>|
|To:||"Fabien COELHO" <coelho(at)cri(dot)ensmp(dot)fr>|
|Cc:||"Ildar Musin" <i(dot)musin(at)postgrespro(dot)ru>,"pgsql-hackers" <pgsql-hackers(at)postgresql(dot)org>|
|Subject:||Re: General purpose hashing func in pgbench|
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Fabien COELHO wrote:
> Most "permutation" functions are really cryptographic cyphers which are
> quite expensive, and require powers of two, which is not what is needed.
> ISTM that there are some constructs to deal with arbitrary sizes based on
> cryptographic functions, but that would make it too expensive for the
FWIW, you might have a look at the permuteseq extension:
It permutes an arbitrary range of 64-bit integers into itself,
with a user-supplied key as the seed.
Outputs are coerced into the desired range by using the
smallest possible power of two for the Feistel cypher's
block size, and then cycle-walking over the results.
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