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: 2021-04-06T11:19:26Z
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 Mon, 5 Apr 2021 at 13:07, Fabien COELHO <coelho@cri.ensmp.fr> wrote:
>
> Attached a v28 which I hope fixes the many above issues and stays with
> ints. The randu64 is still some kind of a joke, I artificially reduced the
> cost by calling jrand48 once and extending it to 64 bits, so it could give
> an idea of the cost endured if a 64-bit prng was used.
>
> Now you are the committer, you can do as you please, I'm just stating my
> (mathematical) opinions about using floating point computations for that.
> I think that apart from this point of principle/philosophy the permute
> performance and implementation are reasonable, and better than my initial
> version because it avoids int128 computations and the large prime number
> business.
>

Pushed.

I decided not to go with the "joke" randu64() function, but instead
used getrand() directly. This at least removes any *direct* use of
doubles in permute() (though of course they're still used indirectly),
and means that if getrand() is improved in the future, permute() will
benefit too.

Regards,
Dean