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

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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
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5
contrib/amcheck/verify_nbtree.c
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@ -32,6 +32,7 @@
#include "catalog/index.h"
#include "catalog/pg_am.h"
#include "commands/tablecmds.h"
#include "common/pg_prng.h"
#include "lib/bloomfilter.h"
#include "miscadmin.h"
#include "storage/lmgr.h"
@ -466,8 +467,8 @@ bt_check_every_level(Relation rel, Relation heaprel, bool heapkeyspace,
total_pages = RelationGetNumberOfBlocks(rel);
total_elems = Max(total_pages * (MaxTIDsPerBTreePage / 3),
(int64) state->rel->rd_rel->reltuples);
/* Random seed relies on backend srandom() call to avoid repetition */
seed = random();
/* Generate a random seed to avoid repetition */
seed = pg_prng_uint64(&pg_global_prng_state);
/* Create Bloom filter to fingerprint index */
state->filter = bloom_create(total_elems, maintenance_work_mem, seed);
state->heaptuplespresent = 0;