Horton

Re: pgbench - add pseudo-random permutation function

Dean Rasheed <dean.a.rasheed@gmail.com>

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From: Dean Rasheed <dean.a.rasheed@gmail.com>
To: Fabien COELHO <coelho@cri.ensmp.fr>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Thomas Munro <thomas.munro@gmail.com>, David Steele <david@pgmasters.net>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Hironobu SUZUKI <hironobu@interdb.jp>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-03-30T19:44:05Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. pgbench: Function to generate random permutations.

  2. Add basic support for using the POPCNT and SSE4.2s LZCNT opcodes

  3. Further improve code for probing the availability of ARM CRC instructions.

On Tue, 30 Mar 2021 at 20:31, Dean Rasheed <dean.a.rasheed@gmail.com> wrote:
>
> Yeah, that's probably a fair point. However, all the existing pgbench
> random functions are using it, so I think it's fair enough for
> permute() to do the same (and actually 2^48 is pretty huge). Switching
> to a 64-bit PRNG might not be a bad idea, but I think that's something
> we'd want to do across the board, and so I think it should be out of
> scope for this patch.
>

Of course the immediate counter-argument to changing the existing
random functions would be that doing so would break lots of people's
tests, and no one would thank us for that. Still, I think that, since
the existing random functions use a 48-bit PRNG, it's not unreasonable
for permute() to do the same.

Regards,
Dean