Horton

Re: pgbench - add pseudo-random permutation function

Bruce Momjian <bruce@momjian.us>

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From: Bruce Momjian <bruce@momjian.us>
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>, Thomas Munro <thomas.munro@gmail.com>, Hironobu SUZUKI <hironobu@interdb.jp>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Dean Rasheed <dean.a.rasheed@gmail.com>
Date: 2021-03-11T00:58:39Z
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 11:50:43AM +0100, Fabien COELHO wrote:
> 
> > > What are your current thoughts?
> > 
> > Thanks for prodding.  I still think it's a useful feature.  However I
> > don't think I'll have to time to get it done on the current commitfest.
> > I suggest to let it sit in the commitfest to see if somebody else will
> > pick it up -- and if not, we move it to the next one, with apologies to
> > author and reviewers.
> > 
> > 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.

Maybe Dean Rasheed can help because of his math background --- CC'ing him.

-- 
  Bruce Momjian  <bruce@momjian.us>        https://momjian.us
  EDB                                      https://enterprisedb.com

  The usefulness of a cup is in its emptiness, Bruce Lee