Horton

Re: pgbench - add pseudo-random permutation function

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Fabien COELHO <coelho@cri.ensmp.fr>
Cc: Alvaro Herrera <alvherre@2ndquadrant.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: 2021-03-12T21:06:48Z
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, Mar 8, 2021 at 11:50 PM Fabien COELHO <coelho@cri.ensmp.fr> wrote:
> > I may have time to become familiar or at least semi-comfortable with all
> > that weird math in it by then.
>
> Yep.
>
> Generating a parametric good-quality low-cost (but not
> cryptographically-secure) pseudo-random permutations on arbitrary sizes
> (not juste power of two sizes) is not a trivial task, I had to be quite
> creative to achieve it, hence the "weird" maths. I had a lot of bad
> not-really-working ideas before the current status of the patch.
>
> The code could be simplified if we assume that PG_INT128_TYPE will be
> available on all relevant architectures, and accept the feature not to be
> available if not.

That doesn't sound like a bad option to me, if it makes this much
simpler.  The main modern system without it seems to be MSVC.  The
Linux, BSD, Apple, illumos, AIX systems using Clang/GCC with
Intel/AMD/ARM/PowerPC CPUs have it, and the Windows systems using open
source compilers have it.