diff --git a/doc/src/sgml/ref/pgbench.sgml b/doc/src/sgml/ref/pgbench.sgml
index 1519fe7..ec07fa3 100644
--- a/doc/src/sgml/ref/pgbench.sgml
+++ b/doc/src/sgml/ref/pgbench.sgml
@@ -680,6 +680,37 @@ pgbench optionsd
+ SEED
+
+
+ Set random generator seed. This random generator is used to initialize
+ per-thread random generator states.
+ Expected values for SEED are:
+ time (the default, the seed is based on the current time),
+ rand (use a strong random source if available),
+ or any unsigned integer value.
+ The random generator is invoked explicitely from a pgbench script
+ (random... functions) or implicitely (for instance option
+ uses random to schedule transactions).
+ The random generator seed may also be provided through environment variable
+ PGBENCH_RANDOM_SEED.
+ To ensure that the provided seed impacts all possible uses, put this option
+ first or use the environment variable.
+
+
+ Setting the seed explicitely allows to reproduce a pgbench
+ run exactly, as far as random numbers are concerned.
+ From a statistical viewpoint this is a bad idea because it can hide the
+ performance variability or improve performance unduly, e.g. by hitting
+ the same pages than a previous run.
+ However it may also be of great help for debugging, for instance
+ re-running a tricky case which leads to an error.
+ Use wisely.
+
+
+
+
+
diff --git a/src/bin/pgbench/pgbench.c b/src/bin/pgbench/pgbench.c
index e065f7b..4eb82f7 100644
--- a/src/bin/pgbench/pgbench.c
+++ b/src/bin/pgbench/pgbench.c
@@ -557,6 +557,7 @@ usage(void)
" --log-prefix=PREFIX prefix for transaction time log file\n"
" (default: \"pgbench_log\")\n"
" --progress-timestamp use Unix epoch timestamps for progress\n"
+ " --random-seed=SEED set random seed (\"time\", \"rand\", integer)\n"
" --sampling-rate=NUM fraction of transactions to log (e.g., 0.01 for 1%%)\n"
"\nCommon options:\n"
" -d, --debug print debugging output\n"
@@ -4010,6 +4011,46 @@ printResults(TState *threads, StatsData *total, instr_time total_time,
}
}
+/* call srandom based on some seed. NULL triggers the default behavior. */
+static void
+set_random_seed(const char *seed)
+{
+ unsigned int iseed;
+
+ if (seed == NULL || *seed == '\0' || strcmp(seed, "time") == 0)
+ {
+ /* rely on current time */
+ instr_time now;
+ INSTR_TIME_SET_CURRENT(now);
+ iseed = (unsigned int) INSTR_TIME_GET_MICROSEC(now);
+ }
+ else if (strcmp(seed, "rand") == 0)
+ {
+ /* use some "strong" random source */
+ if (!pg_strong_random(&iseed, sizeof(iseed)))
+ {
+ fprintf(stderr, "cannot seed random from a strong source\n");
+ exit(1);
+ }
+ }
+ else
+ {
+ /* parse seed value coming either from option or environment */
+ char garbage;
+ if (sscanf(seed, "%u%c", &iseed, &garbage) != 1)
+ {
+ fprintf(stderr,
+ "error while scanning '%s', expecting an unsigned integer\n",
+ seed);
+ exit(1);
+ }
+ }
+
+ if (seed != NULL)
+ fprintf(stderr, "setting random seed to %u\n", iseed);
+ srandom(iseed);
+}
+
int
main(int argc, char **argv)
@@ -4052,6 +4093,7 @@ main(int argc, char **argv)
{"progress-timestamp", no_argument, NULL, 6},
{"log-prefix", required_argument, NULL, 7},
{"foreign-keys", no_argument, NULL, 8},
+ {"random-seed", required_argument, NULL, 9},
{NULL, 0, NULL, 0}
};
@@ -4120,6 +4162,9 @@ main(int argc, char **argv)
state = (CState *) pg_malloc(sizeof(CState));
memset(state, 0, sizeof(CState));
+ /* set random seed early, because it may be used while parsing scripts. */
+ set_random_seed(getenv("PGBENCH_RANDOM_SEED"));
+
while ((c = getopt_long(argc, argv, "iI:h:nvp:dqb:SNc:j:Crs:t:T:U:lf:D:F:M:P:R:L:", long_options, &optindex)) != -1)
{
char *script;
@@ -4392,6 +4437,10 @@ main(int argc, char **argv)
initialization_option_set = true;
foreign_keys = true;
break;
+ case 9: /* random-seed */
+ benchmarking_option_set = true;
+ set_random_seed(optarg);
+ break;
default:
fprintf(stderr, _("Try \"%s --help\" for more information.\n"), progname);
exit(1);
@@ -4698,10 +4747,6 @@ main(int argc, char **argv)
}
PQfinish(con);
- /* set random seed */
- INSTR_TIME_SET_CURRENT(start_time);
- srandom((unsigned int) INSTR_TIME_GET_MICROSEC(start_time));
-
/* set up thread data structures */
threads = (TState *) pg_malloc(sizeof(TState) * nthreads);
nclients_dealt = 0;
diff --git a/src/bin/pgbench/t/001_pgbench_with_server.pl b/src/bin/pgbench/t/001_pgbench_with_server.pl
index 3dd080e..8050f0c 100644
--- a/src/bin/pgbench/t/001_pgbench_with_server.pl
+++ b/src/bin/pgbench/t/001_pgbench_with_server.pl
@@ -210,11 +210,16 @@ COMMIT;
} });
# test expressions
+# command 1..3 and 23 depend on random seed which is used to call srandom.
pgbench(
- '-t 1 -Dfoo=-10.1 -Dbla=false -Di=+3 -Dminint=-9223372036854775808',
+ '--random-seed=5432 -t 1 -Dfoo=-10.1 -Dbla=false -Di=+3 -Dminint=-9223372036854775808',
0,
[ qr{type: .*/001_pgbench_expressions}, qr{processed: 1/1} ],
- [ qr{command=4.: int 4\b},
+ [ qr{setting random seed to 5432\b},
+ qr{command=1.: int 28\b}, # uniform random
+ qr{command=2.: int 7\b}, # exponential random
+ qr{command=3.: int 47\b}, # gaussian random
+ qr{command=4.: int 4\b},
qr{command=5.: int 5\b},
qr{command=6.: int 6\b},
qr{command=7.: int 7\b},
@@ -232,7 +237,7 @@ pgbench(
qr{command=19.: double 19\b},
qr{command=20.: double 20\b},
qr{command=21.: int 9223372036854775807\b},
- qr{command=23.: int [1-9]\b},
+ qr{command=23.: int 1\b}, # zipfian random
qr{command=24.: double -27\b},
qr{command=25.: double 1024\b},
qr{command=26.: double 1\b},