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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2021-11-28 21:32:36 -0500 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2021-11-28 21:33:07 -0500 |
| commit | 3804539e48e794781c6145c7f988f5d507418fa8 (patch) | |
| tree | 317904b43ca8c1d510b23cb8fdd7b05a75e971bc /src/backend/tcop/postgres.c | |
| parent | f44ceb46ec2d8da48f6e145bf462d5620c25e079 (diff) | |
| download | postgresql-3804539e48e794781c6145c7f988f5d507418fa8.tar.gz postgresql-3804539e48e794781c6145c7f988f5d507418fa8.zip | |
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
Diffstat (limited to 'src/backend/tcop/postgres.c')
| -rw-r--r-- | src/backend/tcop/postgres.c | 7 |
1 files changed, 4 insertions, 3 deletions
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) { |