database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-02 09:02:37 +03:00
Code Activity

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

Browse Source 
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
Download Patch File Download Diff File Expand all files Collapse all files

5
src/backend/access/gist/gistutil.c
View File

@ -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;