diff --git a/doc/src/sgml/ref/pgbench.sgml b/doc/src/sgml/ref/pgbench.sgml index 1519fe7..7e81a51 100644 --- a/doc/src/sgml/ref/pgbench.sgml +++ b/doc/src/sgml/ref/pgbench.sgml @@ -680,6 +680,45 @@ pgbench options d + SEED + + + Set random generator seed. Seeds the system random number generator, + which then produces a sequence of initial generator states, one for + each thread. + Values for SEED may be: + time (the default, the seed is based on the current time), + rand (use a strong random source, failing if none + is available), or any unsigned octal (012470), + decimal (5432) or + hexedecimal (0x1538) integer value. + The random generator is invoked explicitly from a pgbench script + (random... functions) or implicitly (for instance option + uses it to schedule transactions). + When explicitely set, the value used for seeding is shown on the terminal. + Any value allowed for SEED may also be + provided through the 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 explicitly allows to reproduce a pgbench + run exactly, as far as random numbers are concerned. + As the random state is managed per thread, this means the exact same + pgbench run for an identical invocation if there is one + client per thread and there are no external or data dependencies. + From a statistical viewpoint reproducing runs exactly is a bad idea because + it can hide the performance variability or improve performance unduly, + e.g. by hitting the same pages as 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 fc2c734..d4ff4c7 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 +4011,55 @@ 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 || 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 uint seed value */ + char garbage; + if (! + /* hexa */ + ((seed[0] == '0' && (seed[1] == 'x' || seed[1] == 'X') && + sscanf(seed, "%x%c", &iseed, &garbage) == 1) || + /* octal */ + (seed[0] == '0' && seed[1] != 'x' && seed[1] != 'X' && + sscanf(seed, "%o%c", &iseed, &garbage) == 1) || + /* decimal */ + (seed[0] != '0' && + sscanf(seed, "%u%c", &iseed, &garbage) == 1))) + { + fprintf(stderr, + "error while scanning '%s', expecting an unsigned integer, 'time' or 'rand'\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 +4102,7 @@ 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 +4171,9 @@ 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 +4446,10 @@ 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 +4756,6 @@ 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..7fee671 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=0x1538 -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}, diff --git a/src/bin/pgbench/t/002_pgbench_no_server.pl b/src/bin/pgbench/t/002_pgbench_no_server.pl index 6ea55f8..6853650 100644 --- a/src/bin/pgbench/t/002_pgbench_no_server.pl +++ b/src/bin/pgbench/t/002_pgbench_no_server.pl @@ -78,6 +78,8 @@ my @options = ( [ 'invalid init step', '-i -I dta', [qr{unrecognized initialization step}, qr{allowed steps are} ] ], + [ 'bad random seed', '--random-seed=one', + [qr{error while scanning 'one', expecting an unsigned integer} ] ], # loging sub-options [ 'sampling => log', '--sampling-rate=0.01',