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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 /contrib/tsm_system_time | |
| 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 'contrib/tsm_system_time')
| -rw-r--r-- | contrib/tsm_system_time/tsm_system_time.c | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/contrib/tsm_system_time/tsm_system_time.c b/contrib/tsm_system_time/tsm_system_time.c index 788d8f9a68..36acc6c106 100644 --- a/contrib/tsm_system_time/tsm_system_time.c +++ b/contrib/tsm_system_time/tsm_system_time.c @@ -69,7 +69,7 @@ static BlockNumber system_time_nextsampleblock(SampleScanState *node, BlockNumbe static OffsetNumber system_time_nextsampletuple(SampleScanState *node, BlockNumber blockno, OffsetNumber maxoffset); -static uint32 random_relative_prime(uint32 n, SamplerRandomState randstate); +static uint32 random_relative_prime(uint32 n, pg_prng_state *randstate); /* @@ -224,25 +224,25 @@ system_time_nextsampleblock(SampleScanState *node, BlockNumber nblocks) if (sampler->step == 0) { /* Initialize now that we have scan descriptor */ - SamplerRandomState randstate; + pg_prng_state randstate; /* If relation is empty, there's nothing to scan */ if (nblocks == 0) return InvalidBlockNumber; /* We only need an RNG during this setup step */ - sampler_random_init_state(sampler->seed, randstate); + sampler_random_init_state(sampler->seed, &randstate); /* Compute nblocks/firstblock/step only once per query */ sampler->nblocks = nblocks; /* Choose random starting block within the relation */ /* (Actually this is the predecessor of the first block visited) */ - sampler->firstblock = sampler_random_fract(randstate) * + sampler->firstblock = sampler_random_fract(&randstate) * sampler->nblocks; /* Find relative prime as step size for linear probing */ - sampler->step = random_relative_prime(sampler->nblocks, randstate); + sampler->step = random_relative_prime(sampler->nblocks, &randstate); } /* Reinitialize lb and start_time */ @@ -330,7 +330,7 @@ gcd(uint32 a, uint32 b) * (else return 1). */ static uint32 -random_relative_prime(uint32 n, SamplerRandomState randstate) +random_relative_prime(uint32 n, pg_prng_state *randstate) { uint32 r; |