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Replace random(), pg_erand48(), etc with a better PRNG API and algorithm.

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Standardize on xoroshiro128** as our basic PRNG algorithm, eliminating
a bunch of platform dependencies as well as fundamentally-obsolete PRNG
code.  In addition, this API replacement will ease replacing the
algorithm again in future, should that become necessary.

xoroshiro128** is a few percent slower than the drand48 family,
but it can produce full-width 64-bit random values not only 48-bit,
and it should be much more trustworthy.  It's likely to be noticeably
faster than the platform's random(), depending on which platform you
are thinking about; and we can have non-global state vectors easily,
unlike with random().  It is not cryptographically strong, but neither
are the functions it replaces.

Fabien Coelho, reviewed by Dean Rasheed, Aleksander Alekseev, and myself

Discussion: https://postgr.es/m/alpine.DEB.2.22.394.2105241211230.165418@pseudo
This commit is contained in:
Tom Lane
2021-11-28 21:32:36 -05:00
parent f44ceb46ec
commit 3804539e48
50 changed files with 543 additions and 480 deletions
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4
contrib/auto_explain/auto_explain.c
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@ -16,6 +16,7 @@
#include "access/parallel.h"
#include "commands/explain.h"
#include "common/pg_prng.h"
#include "executor/instrument.h"
#include "jit/jit.h"
#include "utils/guc.h"
@ -275,8 +276,7 @@ explain_ExecutorStart(QueryDesc *queryDesc, int eflags)
if (nesting_level == 0)
{
if (auto_explain_log_min_duration >= 0 && !IsParallelWorker())
current_query_sampled = (random() < auto_explain_sample_rate *
((double) MAX_RANDOM_VALUE + 1));
current_query_sampled = (pg_prng_double(&pg_global_prng_state) < auto_explain_sample_rate);
else
current_query_sampled = false;
}