Replace random(), pg_erand48(), etc with a better PRNG API and algori…

…thm.

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

configure

@@ -16463,32 +16463,6 @@ esac
 
 fi
 
-ac_fn_c_check_func "$LINENO" "random" "ac_cv_func_random"
-if test "x$ac_cv_func_random" = xyes; then :
-  $as_echo "#define HAVE_RANDOM 1" >>confdefs.h
-
-else
-  case " $LIBOBJS " in
-  *" random.$ac_objext "* ) ;;
-  *) LIBOBJS="$LIBOBJS random.$ac_objext"
- ;;
-esac
-
-fi
-
-ac_fn_c_check_func "$LINENO" "srandom" "ac_cv_func_srandom"
-if test "x$ac_cv_func_srandom" = xyes; then :
-  $as_echo "#define HAVE_SRANDOM 1" >>confdefs.h
-
-else
-  case " $LIBOBJS " in
-  *" srandom.$ac_objext "* ) ;;
-  *) LIBOBJS="$LIBOBJS srandom.$ac_objext"
- ;;
-esac
-
-fi
-
 ac_fn_c_check_func "$LINENO" "strlcat" "ac_cv_func_strlcat"
 if test "x$ac_cv_func_strlcat" = xyes; then :
   $as_echo "#define HAVE_STRLCAT 1" >>confdefs.h

configure.ac

@@ -1858,8 +1858,6 @@ AC_REPLACE_FUNCS(m4_normalize([
 	mkdtemp
 	pread
 	pwrite
-	random
-	srandom
 	strlcat
 	strlcpy
 	strnlen

contrib/amcheck/verify_nbtree.c

@@ -32,6 +32,7 @@
 #include "catalog/index.h"
 #include "catalog/pg_am.h"
 #include "commands/tablecmds.h"
+#include "common/pg_prng.h"
 #include "lib/bloomfilter.h"
 #include "miscadmin.h"
 #include "storage/lmgr.h"
@@ -466,8 +467,8 @@ bt_check_every_level(Relation rel, Relation heaprel, bool heapkeyspace,
 		total_pages = RelationGetNumberOfBlocks(rel);
 		total_elems = Max(total_pages * (MaxTIDsPerBTreePage / 3),
 						  (int64) state->rel->rd_rel->reltuples);
-		/* Random seed relies on backend srandom() call to avoid repetition */
-		seed = random();
+		/* Generate a random seed to avoid repetition */
+		seed = pg_prng_uint64(&pg_global_prng_state);
 		/* Create Bloom filter to fingerprint index */
 		state->filter = bloom_create(total_elems, maintenance_work_mem, seed);
 		state->heaptuplespresent = 0;

contrib/auto_explain/auto_explain.c

@@ -16,6 +16,7 @@
 
 #include "access/parallel.h"
 #include "commands/explain.h"
+#include "common/pg_prng.h"
 #include "executor/instrument.h"
 #include "jit/jit.h"
 #include "utils/guc.h"
@@ -275,8 +276,7 @@ explain_ExecutorStart(QueryDesc *queryDesc, int eflags)
 	if (nesting_level == 0)
 	{
 		if (auto_explain_log_min_duration >= 0 && !IsParallelWorker())
-			current_query_sampled = (random() < auto_explain_sample_rate *
-									 ((double) MAX_RANDOM_VALUE + 1));
+			current_query_sampled = (pg_prng_double(&pg_global_prng_state) < auto_explain_sample_rate);
 		else
 			current_query_sampled = false;
 	}

contrib/file_fdw/file_fdw.c

@@ -1188,7 +1188,7 @@ file_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]);

contrib/postgres_fdw/postgres_fdw.c

@@ -5158,7 +5158,7 @@ analyze_row_processor(PGresult *res, int row, PgFdwAnalyzeState *astate)
 		if (astate->rowstoskip <= 0)
 		{
 			/* Choose a random reservoir element to replace. */
-			pos = (int) (targrows * sampler_random_fract(astate->rstate.randstate));
+			pos = (int) (targrows * sampler_random_fract(&astate->rstate.randstate));
 			Assert(pos >= 0 && pos < targrows);
 			heap_freetuple(astate->rows[pos]);
 		}

contrib/tablefunc/tablefunc.c

@@ -36,6 +36,7 @@
 
 #include "access/htup_details.h"
 #include "catalog/pg_type.h"
+#include "common/pg_prng.h"
 #include "executor/spi.h"
 #include "funcapi.h"
 #include "lib/stringinfo.h"
@@ -290,8 +291,8 @@ get_normal_pair(float8 *x1, float8 *x2)
 
 	do
 	{
-		u1 = (float8) random() / (float8) MAX_RANDOM_VALUE;
-		u2 = (float8) random() / (float8) MAX_RANDOM_VALUE;
+		u1 = pg_prng_double(&pg_global_prng_state);
+		u2 = pg_prng_double(&pg_global_prng_state);
 
 		v1 = (2.0 * u1) - 1.0;
 		v2 = (2.0 * u2) - 1.0;

contrib/tsm_system_rows/tsm_system_rows.c

@@ -69,7 +69,7 @@ static BlockNumber system_rows_nextsampleblock(SampleScanState *node, BlockNumbe
 static OffsetNumber system_rows_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);
 
 
 /*
@@ -213,25 +213,25 @@ system_rows_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 */
@@ -317,7 +317,7 @@ 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;
 

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;
 

src/backend/access/gin/ginget.c

@@ -16,6 +16,7 @@
 
 #include "access/gin_private.h"
 #include "access/relscan.h"
+#include "common/pg_prng.h"
 #include "miscadmin.h"
 #include "storage/predicate.h"
 #include "utils/datum.h"
@@ -787,7 +788,7 @@ entryLoadMoreItems(GinState *ginstate, GinScanEntry entry,
 	}
 }
 
-#define gin_rand() (((double) random()) / ((double) MAX_RANDOM_VALUE))
+#define gin_rand() pg_prng_double(&pg_global_prng_state)
 #define dropItem(e) ( gin_rand() > ((double)GinFuzzySearchLimit)/((double)((e)->predictNumberResult)) )
 
 /*

src/backend/access/gist/gistutil.c

@@ -19,6 +19,7 @@
 #include "access/htup_details.h"
 #include "access/reloptions.h"
 #include "catalog/pg_opclass.h"
+#include "common/pg_prng.h"
 #include "storage/indexfsm.h"
 #include "storage/lmgr.h"
 #include "utils/float.h"
@@ -507,7 +508,7 @@ gistchoose(Relation r, Page p, IndexTuple it,	/* it has compressed entry */
 			if (keep_current_best == -1)
 			{
 				/* we didn't make the random choice yet for this old best */
-				keep_current_best = (random() <= (MAX_RANDOM_VALUE / 2)) ? 1 : 0;
+				keep_current_best = pg_prng_bool(&pg_global_prng_state) ? 1 : 0;
 			}
 			if (keep_current_best == 0)
 			{
@@ -529,7 +530,7 @@ gistchoose(Relation r, Page p, IndexTuple it,	/* it has compressed entry */
 			if (keep_current_best == -1)
 			{
 				/* we didn't make the random choice yet for this old best */
-				keep_current_best = (random() <= (MAX_RANDOM_VALUE / 2)) ? 1 : 0;
+				keep_current_best = pg_prng_bool(&pg_global_prng_state) ? 1 : 0;
 			}
 			if (keep_current_best == 1)
 				break;

src/backend/access/nbtree/nbtinsert.c

@@ -19,6 +19,7 @@
 #include "access/nbtxlog.h"
 #include "access/transam.h"
 #include "access/xloginsert.h"
+#include "common/pg_prng.h"
 #include "lib/qunique.h"
 #include "miscadmin.h"
 #include "storage/lmgr.h"
@@ -965,7 +966,7 @@ _bt_findinsertloc(Relation rel,
 
 			if (P_RIGHTMOST(opaque) ||
 				_bt_compare(rel, itup_key, page, P_HIKEY) != 0 ||
-				random() <= (MAX_RANDOM_VALUE / 100))
+				pg_prng_uint32(&pg_global_prng_state) <= (PG_UINT32_MAX / 100))
 				break;
 
 			_bt_stepright(rel, insertstate, stack);

src/backend/access/spgist/spgdoinsert.c

@@ -19,6 +19,7 @@
 #include "access/spgist_private.h"
 #include "access/spgxlog.h"
 #include "access/xloginsert.h"
+#include "common/pg_prng.h"
 #include "miscadmin.h"
 #include "storage/bufmgr.h"
 #include "utils/rel.h"
@@ -2210,7 +2211,9 @@ spgdoinsert(Relation index, SpGistState *state,
 				if (out.resultType == spgAddNode)
 					elog(ERROR, "cannot add a node to an allTheSame inner tuple");
 				else if (out.resultType == spgMatchNode)
-					out.result.matchNode.nodeN = random() % innerTuple->nNodes;
+					out.result.matchNode.nodeN =
+						pg_prng_uint64_range(&pg_global_prng_state,
+											 0, innerTuple->nNodes - 1);
 			}
 
 			switch (out.resultType)

src/backend/access/transam/xact.c

@@ -37,6 +37,7 @@
 #include "commands/async.h"
 #include "commands/tablecmds.h"
 #include "commands/trigger.h"
+#include "common/pg_prng.h"
 #include "executor/spi.h"
 #include "libpq/be-fsstubs.h"
 #include "libpq/pqsignal.h"
@@ -1990,7 +1991,7 @@ StartTransaction(void)
 	/* Determine if statements are logged in this transaction */
 	xact_is_sampled = log_xact_sample_rate != 0 &&
 		(log_xact_sample_rate == 1 ||
-		 random() <= log_xact_sample_rate * MAX_RANDOM_VALUE);
+		 pg_prng_double(&pg_global_prng_state) <= log_xact_sample_rate);
 
 	/*
 	 * initialize current transaction state fields

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]);

src/backend/executor/nodeSamplescan.c

@@ -17,6 +17,7 @@
 #include "access/relscan.h"
 #include "access/tableam.h"
 #include "access/tsmapi.h"
+#include "common/pg_prng.h"
 #include "executor/executor.h"
 #include "executor/nodeSamplescan.h"
 #include "miscadmin.h"
@@ -154,7 +155,7 @@ ExecInitSampleScan(SampleScan *node, EState *estate, int eflags)
 	 * do this just once, since the seed shouldn't change over rescans.
 	 */
 	if (tsc->repeatable == NULL)
-		scanstate->seed = random();
+		scanstate->seed = pg_prng_uint32(&pg_global_prng_state);
 
 	/*
 	 * Finally, initialize the TABLESAMPLE method handler.

src/backend/lib/bloomfilter.c

@@ -81,8 +81,7 @@ static inline uint32 mod_m(uint32 a, uint64 m);
  * distinct seed value on every call makes it unlikely that the same false
  * positives will reoccur when the same set is fingerprinted a second time.
  * Callers that don't care about this pass a constant as their seed, typically
- * 0.  Callers can use a pseudo-random seed in the range of 0 - INT_MAX by
- * calling random().
+ * 0.  Callers can also use a pseudo-random seed, eg from pg_prng_uint64().
  */
 bloom_filter *
 bloom_create(int64 total_elems, int bloom_work_mem, uint64 seed)