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 --- src/backend/tcop/postgres.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'src/backend/tcop/postgres.c') diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c index 0775abe35de..82de01cdc67 100644 --- a/src/backend/tcop/postgres.c +++ b/src/backend/tcop/postgres.c @@ -42,6 +42,7 @@ #include "catalog/pg_type.h" #include "commands/async.h" #include "commands/prepare.h" +#include "common/pg_prng.h" #include "executor/spi.h" #include "jit/jit.h" #include "libpq/libpq.h" @@ -2355,13 +2356,13 @@ check_log_duration(char *msec_str, bool was_logged) /* * Do not log if log_statement_sample_rate = 0. Log a sample if - * log_statement_sample_rate <= 1 and avoid unnecessary random() call - * if log_statement_sample_rate = 1. + * log_statement_sample_rate <= 1 and avoid unnecessary PRNG call if + * log_statement_sample_rate = 1. */ if (exceeded_sample_duration) in_sample = log_statement_sample_rate != 0 && (log_statement_sample_rate == 1 || - random() <= log_statement_sample_rate * MAX_RANDOM_VALUE); + pg_prng_double(&pg_global_prng_state) <= log_statement_sample_rate); if (exceeded_duration || in_sample || log_duration || xact_is_sampled) { -- cgit v1.2.3