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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
src/backend/storage/lmgr/Makefile
View File

@@ -30,9 +30,10 @@ ifdef TAS
TASPATH = $(top_builddir)/src/backend/port/tas.o
endif
s_lock_test: s_lock.c $(top_builddir)/src/port/libpgport.a
s_lock_test: s_lock.c $(top_builddir)/src/common/libpgcommon.a $(top_builddir)/src/port/libpgport.a
$(CC) $(CPPFLAGS) $(CFLAGS) -DS_LOCK_TEST=1 $(srcdir)/s_lock.c \
$(TASPATH) -L $(top_builddir)/src/port -lpgport -o s_lock_test
$(TASPATH) -L $(top_builddir)/src/common -lpgcommon \
-L $(top_builddir)/src/port -lpgport -o s_lock_test
# see notes in src/backend/parser/Makefile
lwlocknames.c: lwlocknames.h

5
src/backend/storage/lmgr/s_lock.c
View File

@@ -50,6 +50,7 @@
#include <time.h>
#include <unistd.h>
#include "common/pg_prng.h"
#include "port/atomics.h"
#include "storage/s_lock.h"
@@ -144,7 +145,7 @@ perform_spin_delay(SpinDelayStatus *status)
/* increase delay by a random fraction between 1X and 2X */
status->cur_delay += (int) (status->cur_delay *
((double) random() / (double) MAX_RANDOM_VALUE) + 0.5);
pg_prng_double(&pg_global_prng_state) + 0.5);
/* wrap back to minimum delay when max is exceeded */
if (status->cur_delay > MAX_DELAY_USEC)
status->cur_delay = MIN_DELAY_USEC;
@@ -303,7 +304,7 @@ volatile struct test_lock_struct test_lock;
int
main()
{
srandom((unsigned int) time(NULL));
pg_prng_seed(&pg_global_prng_state, (uint64) time(NULL));
test_lock.pad1 = test_lock.pad2 = 0x44;