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authorTom Lane <tgl@sss.pgh.pa.us>2021-11-28 21:32:36 -0500
committerTom Lane <tgl@sss.pgh.pa.us>2021-11-28 21:33:07 -0500
commit3804539e48e794781c6145c7f988f5d507418fa8 (patch)
tree317904b43ca8c1d510b23cb8fdd7b05a75e971bc /src/backend/commands/analyze.c
parentf44ceb46ec2d8da48f6e145bf462d5620c25e079 (diff)
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/commands/analyze.c')
-rw-r--r--src/backend/commands/analyze.c7
1 files changed, 4 insertions, 3 deletions
diff --git a/src/backend/commands/analyze.c b/src/backend/commands/analyze.c
index 4928702aec0..cd77907fc74 100644
--- a/src/backend/commands/analyze.c
+++ b/src/backend/commands/analyze.c
@@ -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]);