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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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7
src/backend/commands/analyze.c
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@@ -38,6 +38,7 @@
#include "commands/progress.h"
#include "commands/tablecmds.h"
#include "commands/vacuum.h"
#include "common/pg_prng.h"
#include "executor/executor.h"
#include "foreign/fdwapi.h"
#include "miscadmin.h"
@@ -1140,7 +1141,7 @@ acquire_sample_rows(Relation onerel, int elevel,
double liverows = 0; /* # live rows seen */
double deadrows = 0; /* # dead rows seen */
double rowstoskip = -1; /* -1 means not set yet */
long randseed; /* Seed for block sampler(s) */
uint32 randseed; /* Seed for block sampler(s) */
BlockNumber totalblocks;
TransactionId OldestXmin;
BlockSamplerData bs;
@@ -1162,7 +1163,7 @@ acquire_sample_rows(Relation onerel, int elevel,
OldestXmin = GetOldestNonRemovableTransactionId(onerel);
/* Prepare for sampling block numbers */
randseed = random();
randseed = pg_prng_uint32(&pg_global_prng_state);
nblocks = BlockSampler_Init(&bs, totalblocks, targrows, randseed);
#ifdef USE_PREFETCH
@@ -1279,7 +1280,7 @@ acquire_sample_rows(Relation onerel, int elevel,
* Found a suitable tuple, so save it, replacing one old
* tuple at random
*/
int k = (int) (targrows * sampler_random_fract(rstate.randstate));
int k = (int) (targrows * sampler_random_fract(&rstate.randstate));
Assert(k >= 0 && k < targrows);
heap_freetuple(rows[k]);