diff options
author | Tom Lane <tgl@sss.pgh.pa.us> | 2021-11-28 21:32:36 -0500 |
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committer | Tom Lane <tgl@sss.pgh.pa.us> | 2021-11-28 21:33:07 -0500 |
commit | 3804539e48e794781c6145c7f988f5d507418fa8 (patch) | |
tree | 317904b43ca8c1d510b23cb8fdd7b05a75e971bc /src/backend/commands/analyze.c | |
parent | f44ceb46ec2d8da48f6e145bf462d5620c25e079 (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.c | 7 |
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]); |