Horton

Re: random() (was Re: New GUC to sample log queries)

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Adrien Nayrat <adrien.nayrat@anayrat.info>, Thomas Munro <thomas.munro@enterprisedb.com>, Dmitry Dolgov <9erthalion6@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Vik Fearing <vik.fearing@2ndquadrant.com>, Robert Haas <robertmhaas@gmail.com>, Michael Paquier <michael@paquier.xyz>, David Rowley <david.rowley@2ndquadrant.com>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2018-12-26T20:19:15Z
Lists: pgsql-hackers 
Peter Geoghegan <pg@bowt.ie> writes:
> I'm beginning to think that the technique that I came up with to make
> "getting tired" deterministic ought to be supporting as a debugging
> option if we're to do away with internal use of the generic/seedable
> backend PRNG.

I have no objection to providing such a thing as a debug option; I just
don't want it to be reachable from SQL (at least not without pieces
that aren't there normally, e.g. a loadable C function).

Replacing random() might actually make that easier not harder, since
we'd have more control over what happens when.

			regards, tom lane

Commits

  1. Use pg_strong_random() to select each server process's random seed.

  2. Use a separate random seed for SQL random()/setseed() functions.

  3. Marginal performance hacking in erand48.c.

  4. Fix latent problem with pg_jrand48().

  5. Silence compiler warning

  6. Add log_statement_sample_rate parameter