From 3804539e48e794781c6145c7f988f5d507418fa8 Mon Sep 17 00:00:00 2001
From: Tom Lane
Date: Sun, 28 Nov 2021 21:32:36 -0500
Subject: Replace random(), pg_erand48(), etc with a better PRNG API and
 algorithm.

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
---
 contrib/auto_explain/auto_explain.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

(limited to 'contrib/auto_explain')

diff --git a/contrib/auto_explain/auto_explain.c b/contrib/auto_explain/auto_explain.c
index e9092ba359a..59ba63455fd 100644
--- a/contrib/auto_explain/auto_explain.c
+++ b/contrib/auto_explain/auto_explain.c
@@ -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;
 	}
-- 
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