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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/access/gist/gistutil.c | |
| parent | f44ceb46ec2d8da48f6e145bf462d5620c25e079 (diff) | |
| download | postgresql-3804539e48e794781c6145c7f988f5d507418fa8.tar.gz | |
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/access/gist/gistutil.c')
| -rw-r--r-- | src/backend/access/gist/gistutil.c | 5 |
1 files changed, 3 insertions, 2 deletions
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; |