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/access/gist/gistutil.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'src/backend/access/gist/gistutil.c') diff --git a/src/backend/access/gist/gistutil.c b/src/backend/access/gist/gistutil.c index 43ba03b6eb..94dbabc198 100644 --- a/src/backend/access/gist/gistutil.c +++ b/src/backend/access/gist/gistutil.c @@ -19,6 +19,7 @@ #include "access/htup_details.h" #include "access/reloptions.h" #include "catalog/pg_opclass.h" +#include "common/pg_prng.h" #include "storage/indexfsm.h" #include "storage/lmgr.h" #include "utils/float.h" @@ -507,7 +508,7 @@ gistchoose(Relation r, Page p, IndexTuple it, /* it has compressed entry */ if (keep_current_best == -1) { /* we didn't make the random choice yet for this old best */ - keep_current_best = (random() <= (MAX_RANDOM_VALUE / 2)) ? 1 : 0; + keep_current_best = pg_prng_bool(&pg_global_prng_state) ? 1 : 0; } if (keep_current_best == 0) { @@ -529,7 +530,7 @@ gistchoose(Relation r, Page p, IndexTuple it, /* it has compressed entry */ if (keep_current_best == -1) { /* we didn't make the random choice yet for this old best */ - keep_current_best = (random() <= (MAX_RANDOM_VALUE / 2)) ? 1 : 0; + keep_current_best = pg_prng_bool(&pg_global_prng_state) ? 1 : 0; } if (keep_current_best == 1) break; -- cgit v1.2.1