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Commit4af43ee

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Make pgbench use erand48() rather than random().
glibc renders random() thread-safe by wrapping a futex lock around it;testing reveals that this limits the performance of pgbench on machineswith many CPU cores. Rather than switching to random_r(), which isonly available on GNU systems and crashes unless you use undocumentedalchemy to initialize the random state properly, switch to our built-inimplementation of erand48(), which is both thread-safe and concurrent.Since the list of reasons not to use the operating system's erand48()is getting rather long, rename ours to pg_erand48() (and similarlyfor our implementations of lrand48() and srand48()) and just alwaysuse those. We were already doing this on Cygwin anyway, and theglibc implementation is not quite thread-safe, so pgbench wouldn'tbe able to use that either.Per discussion with Tom Lane.
1 parentac36e6f commit4af43ee

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12 files changed

+40
-62
lines changed

12 files changed

+40
-62
lines changed

‎configure‎

Lines changed: 1 addition & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -20493,8 +20493,7 @@ LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
2049320493

2049420494

2049520495

20496-
20497-
for ac_func in crypt erand48 getopt getrusage inet_aton random rint srandom strdup strerror strlcat strlcpy strtol strtoul
20496+
for ac_func in crypt getopt getrusage inet_aton random rint srandom strdup strerror strlcat strlcpy strtol strtoul
2049820497
do
2049920498
as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
2050020499
{ $as_echo "$as_me:$LINENO: checking for $ac_func" >&5
@@ -21010,17 +21009,6 @@ esac
2101021009

2101121010
fi
2101221011

21013-
# Cygwin's erand48() is broken (always returns zero) in some releases,
21014-
# so force use of ours.
21015-
if test "$PORTNAME" = "cygwin"; then
21016-
case " $LIBOBJS " in
21017-
*" erand48.$ac_objext "* ) ;;
21018-
*) LIBOBJS="$LIBOBJS erand48.$ac_objext"
21019-
;;
21020-
esac
21021-
21022-
fi
21023-
2102421012
# Win32 support
2102521013
if test "$PORTNAME" = "win32"; then
2102621014

‎configure.in‎

Lines changed: 1 addition & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -1311,7 +1311,7 @@ fi
13111311
pgac_save_LIBS="$LIBS"
13121312
LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
13131313

1314-
AC_REPLACE_FUNCS([crypterand48getopt getrusage inet_aton random rint srandom strdup strerror strlcat strlcpy strtol strtoul])
1314+
AC_REPLACE_FUNCS([crypt getopt getrusage inet_aton random rint srandom strdup strerror strlcat strlcpy strtol strtoul])
13151315

13161316
case $host_os in
13171317

@@ -1362,12 +1362,6 @@ if test "$PORTNAME" = "win32"; then
13621362
AC_LIBOBJ(getopt_long)
13631363
fi
13641364

1365-
# Cygwin's erand48() is broken (always returns zero) in some releases,
1366-
# so force use of ours.
1367-
if test "$PORTNAME" = "cygwin"; then
1368-
AC_LIBOBJ(erand48)
1369-
fi
1370-
13711365
# Win32 support
13721366
if test "$PORTNAME" = "win32"; then
13731367
AC_REPLACE_FUNCS(gettimeofday)

‎contrib/pgbench/pgbench.c‎

Lines changed: 15 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -198,6 +198,7 @@ typedef struct
198198
instr_timestart_time;/* thread start time */
199199
instr_time*exec_elapsed;/* time spent executing cmds (per Command) */
200200
int*exec_count;/* number of cmd executions (per Command) */
201+
unsigned shortrandom_state[3];/* separate randomness for each thread */
201202
}TState;
202203

203204
#defineINVALID_THREAD((pthread_t) 0)
@@ -380,13 +381,18 @@ usage(const char *progname)
380381

381382
/* random number generator: uniform distribution from min to max inclusive */
382383
staticint
383-
getrand(intmin,intmax)
384+
getrand(TState*thread,intmin,intmax)
384385
{
385386
/*
386387
* Odd coding is so that min and max have approximately the same chance of
387388
* being selected as do numbers between them.
389+
*
390+
* pg_erand48() is thread-safe and concurrent, which is why we use it
391+
* rather than random(), which in glibc is non-reentrant, and therefore
392+
* protected by a mutex, and therefore a bottleneck on machines with many
393+
* CPUs.
388394
*/
389-
returnmin+ (int) (((max-min+1)*(double)random()) / (MAX_RANDOM_VALUE+1.0));
395+
returnmin+ (int) ((max-min+1)*pg_erand48(thread->random_state));
390396
}
391397

392398
/* call PQexec() and exit() on failure */
@@ -901,7 +907,7 @@ doCustom(TState *thread, CState *st, instr_time *conn_time, FILE *logfile)
901907
if (commands[st->state]==NULL)
902908
{
903909
st->state=0;
904-
st->use_file=getrand(0,num_files-1);
910+
st->use_file=getrand(thread,0,num_files-1);
905911
commands=sql_files[st->use_file];
906912
}
907913
}
@@ -1068,9 +1074,9 @@ doCustom(TState *thread, CState *st, instr_time *conn_time, FILE *logfile)
10681074
}
10691075

10701076
#ifdefDEBUG
1071-
printf("min: %d max: %d random: %d\n",min,max,getrand(min,max));
1077+
printf("min: %d max: %d random: %d\n",min,max,getrand(thread,min,max));
10721078
#endif
1073-
snprintf(res,sizeof(res),"%d",getrand(min,max));
1079+
snprintf(res,sizeof(res),"%d",getrand(thread,min,max));
10741080

10751081
if (!putVariable(st,argv[0],argv[1],res))
10761082
{
@@ -2242,6 +2248,9 @@ main(int argc, char **argv)
22422248
thread->tid=i;
22432249
thread->state=&state[nclients /nthreads*i];
22442250
thread->nstate=nclients /nthreads;
2251+
thread->random_state[0]=random();
2252+
thread->random_state[1]=random();
2253+
thread->random_state[2]=random();
22452254

22462255
if (is_latencies)
22472256
{
@@ -2384,7 +2393,7 @@ threadRun(void *arg)
23842393
Command**commands=sql_files[st->use_file];
23852394
intprev_ecnt=st->ecnt;
23862395

2387-
st->use_file=getrand(0,num_files-1);
2396+
st->use_file=getrand(thread,0,num_files-1);
23882397
if (!doCustom(thread,st,&result->conn_time,logfile))
23892398
remains--;/* I've aborted */
23902399

@@ -2583,17 +2592,6 @@ pthread_create(pthread_t *thread,
25832592
if (duration>0)
25842593
setalarm(duration);
25852594

2586-
/*
2587-
* Set a different random seed in each child process. Otherwise they all
2588-
* inherit the parent's state and generate the same "random" sequence. (In
2589-
* the threaded case, the different threads will obtain subsets of the
2590-
* output of a single random() sequence, which should be okay for our
2591-
* purposes.)
2592-
*/
2593-
INSTR_TIME_SET_CURRENT(start_time);
2594-
srandom(((unsignedint)INSTR_TIME_GET_MICROSEC(start_time))+
2595-
((unsignedint)getpid()));
2596-
25972595
ret=start_routine(arg);
25982596
write(th->pipes[1],ret,sizeof(TResult));
25992597
close(th->pipes[1]);

‎src/backend/optimizer/geqo/geqo_random.c‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -36,5 +36,5 @@ geqo_rand(PlannerInfo *root)
3636
{
3737
GeqoPrivateData*private= (GeqoPrivateData*)root->join_search_private;
3838

39-
returnerand48(private->random_state);
39+
returnpg_erand48(private->random_state);
4040
}

‎src/backend/optimizer/geqo/geqo_selection.c‎

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -64,9 +64,9 @@ geqo_selection(PlannerInfo *root, Chromosome *momma, Chromosome *daddy,
6464
* Ensure we have selected different genes, except if pool size is only
6565
* one, when we can't.
6666
*
67-
* This codehas been observed to hang up in an infinite loop when the
68-
* platform's implementation of erand48()is broken. Weconsider that a
69-
*feature: it lets you know you'd better fix the random-number generator.
67+
* This codewas observed to hang up in an infinite loop when the
68+
* platform's implementation of erand48()was broken. Wenow always
69+
*use our own version.
7070
*/
7171
if (pool->size>1)
7272
{

‎src/include/optimizer/geqo.h‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -73,7 +73,7 @@ extern double Geqo_seed;/* 0 .. 1 */
7373
typedefstruct
7474
{
7575
List*initial_rels;/* the base relations we are joining */
76-
unsigned shortrandom_state[3];/* state forerand48() */
76+
unsigned shortrandom_state[3];/* state forpg_erand48() */
7777
}GeqoPrivateData;
7878

7979

‎src/include/pg_config.h.in‎

Lines changed: 0 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -149,9 +149,6 @@
149149
/* Define to 1 if you have the <editline/readline.h> header file. */
150150
#undef HAVE_EDITLINE_READLINE_H
151151

152-
/* Define to 1 if you have the `erand48' function. */
153-
#undef HAVE_ERAND48
154-
155152
/* Define to 1 if you have the `ERR_set_mark' function. */
156153
#undef HAVE_ERR_SET_MARK
157154

‎src/include/port.h‎

Lines changed: 3 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -380,12 +380,9 @@ extern off_t ftello(FILE *stream);
380380
#endif
381381
#endif
382382

383-
#ifndefHAVE_ERAND48
384-
/* we assume all of these are present or missing together */
385-
externdoubleerand48(unsigned shortxseed[3]);
386-
externlonglrand48(void);
387-
externvoidsrand48(longseed);
388-
#endif
383+
externdoublepg_erand48(unsigned shortxseed[3]);
384+
externlongpg_lrand48(void);
385+
externvoidpg_srand48(longseed);
389386

390387
#ifndefHAVE_FSEEKO
391388
#definefseeko(a,b,c) fseek(a, b, c)

‎src/port/Makefile‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -30,8 +30,8 @@ include $(top_builddir)/src/Makefile.global
3030
overrideCPPFLAGS := -I$(top_builddir)/src/port -DFRONTEND$(CPPFLAGS)
3131
LIBS +=$(PTHREAD_LIBS)
3232

33-
OBJS =$(LIBOBJS) chklocale.o dirmod.oexec.oinet_net_ntop.onoblock.o\
34-
path.o pgcheckdir.o pgmkdirp.o pgsleep.o pgstrcasecmp.o\
33+
OBJS =$(LIBOBJS) chklocale.o dirmod.oerand48.oexec.oinet_net_ntop.o\
34+
noblock.opath.o pgcheckdir.o pgmkdirp.o pgsleep.o pgstrcasecmp.o\
3535
qsort.o qsort_arg.o sprompt.o thread.o
3636

3737
# foo_srv.o and foo.o are both built from foo.c, but only foo.o has -DFRONTEND

‎src/port/erand48.c‎

Lines changed: 11 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -2,10 +2,14 @@
22
*
33
* erand48.c
44
*
5-
* This file supplies versions of erand48(), lrand48(), and srand48()
6-
* for machines that lack them. (These are all the members of the drand48
7-
* family that Postgres currently requires. We name the file after erand48
8-
* because that is the one that configure tests for.)
5+
* This file supplies pg_erand48(), pg_lrand48(), and pg_srand48(), which
6+
* are just like erand48(), lrand48(), and srand48() except that we use
7+
* our own implementation rather than the one provided by the operating
8+
* system. We used to test for an operating system version rather than
9+
* unconditionally using our own, but (1) some versions of Cygwin have a
10+
* buggy erand48() that always returns zero and (2) as of 2011, glibc's
11+
* erand48() is strangely coded to be almost-but-not-quite thread-safe,
12+
* which doesn't matter for the backend but is important for pgbench.
913
*
1014
*
1115
* Copyright (c) 1993 Martin Birgmeier
@@ -72,7 +76,7 @@ _dorand48(unsigned short xseed[3])
7276

7377

7478
double
75-
erand48(unsigned shortxseed[3])
79+
pg_erand48(unsigned shortxseed[3])
7680
{
7781
_dorand48(xseed);
7882
returnldexp((double)xseed[0],-48)+
@@ -81,14 +85,14 @@ erand48(unsigned short xseed[3])
8185
}
8286

8387
long
84-
lrand48(void)
88+
pg_lrand48(void)
8589
{
8690
_dorand48(_rand48_seed);
8791
return ((long)_rand48_seed[2] <<15)+ ((long)_rand48_seed[1] >>1);
8892
}
8993

9094
void
91-
srand48(longseed)
95+
pg_srand48(longseed)
9296
{
9397
_rand48_seed[0]=RAND48_SEED_0;
9498
_rand48_seed[1]= (unsigned short)seed;

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