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Commit64f8589

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Set random seed for pgbench.
Setting random could increase reproducibility of test in some cases. Patchsuggests three providers for seed: time (default), strong randomgenerator (if available) and unsigned constant. Seed could be set fromcommand line or enviroment variable.Author: Fabien CoelhoReviewed by: Chapman FlackDiscussion:https://www.postgresql.org/message-id/flat/20160407082711.q7iq3ykffqxcszkv@alap3.anarazel.de
1 parent530bcf7 commit64f8589

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4 files changed

+170
-12
lines changed

4 files changed

+170
-12
lines changed

‎doc/src/sgml/ref/pgbench.sgml

Lines changed: 42 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -679,6 +679,43 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d
679679
</listitem>
680680
</varlistentry>
681681

682+
<varlistentry>
683+
<term><option>--random-seed=</option><replaceable>SEED</replaceable></term>
684+
<listitem>
685+
<para>
686+
Set random generator seed. Seeds the system random number generator,
687+
which then produces a sequence of initial generator states, one for
688+
each thread.
689+
Values for <replaceable>SEED</replaceable> may be:
690+
<literal>time</literal> (the default, the seed is based on the current time),
691+
<literal>rand</literal> (use a strong random source, failing if none
692+
is available), or an unsigned decimal integer value.
693+
The random generator is invoked explicitly from a pgbench script
694+
(<literal>random...</literal> functions) or implicitly (for instance option
695+
<option>--rate</option> uses it to schedule transactions).
696+
When explicitly set, the value used for seeding is shown on the terminal.
697+
Any value allowed for <replaceable>SEED</replaceable> may also be
698+
provided through the environment variable
699+
<literal>PGBENCH_RANDOM_SEED</literal>.
700+
To ensure that the provided seed impacts all possible uses, put this option
701+
first or use the environment variable.
702+
</para>
703+
<para>
704+
Setting the seed explicitly allows to reproduce a <command>pgbench</command>
705+
run exactly, as far as random numbers are concerned.
706+
As the random state is managed per thread, this means the exact same
707+
<command>pgbench</command> run for an identical invocation if there is one
708+
client per thread and there are no external or data dependencies.
709+
From a statistical viewpoint reproducing runs exactly is a bad idea because
710+
it can hide the performance variability or improve performance unduly,
711+
e.g. by hitting the same pages as a previous run.
712+
However, it may also be of great help for debugging, for instance
713+
re-running a tricky case which leads to an error.
714+
Use wisely.
715+
</para>
716+
</listitem>
717+
</varlistentry>
718+
682719
<varlistentry>
683720
<term><option>--sampling-rate=<replaceable>rate</replaceable></option></term>
684721
<listitem>
@@ -883,6 +920,11 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d
883920
<entry>seed used in hash functions by default</entry>
884921
</row>
885922

923+
<row>
924+
<entry> <literal>random_seed</literal> </entry>
925+
<entry>random generator seed (unless overwritten with <option>-D</option>)</entry>
926+
</row>
927+
886928
<row>
887929
<entry> <literal>scale</literal> </entry>
888930
<entry>current scale factor</entry>

‎src/bin/pgbench/pgbench.c

Lines changed: 63 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -155,6 +155,9 @@ int64latency_limit = 0;
155155
char*tablespace=NULL;
156156
char*index_tablespace=NULL;
157157

158+
/* random seed used when calling srandom() */
159+
int64random_seed=-1;
160+
158161
/*
159162
* end of configurable parameters
160163
*********************************************************************/
@@ -579,6 +582,7 @@ usage(void)
579582
" --log-prefix=PREFIX prefix for transaction time log file\n"
580583
" (default: \"pgbench_log\")\n"
581584
" --progress-timestamp use Unix epoch timestamps for progress\n"
585+
" --random-seed=SEED set random seed (\"time\", \"rand\", integer)\n"
582586
" --sampling-rate=NUM fraction of transactions to log (e.g., 0.01 for 1%%)\n"
583587
"\nCommon options:\n"
584588
" -d, --debug print debugging output\n"
@@ -4664,6 +4668,49 @@ printResults(TState *threads, StatsData *total, instr_time total_time,
46644668
}
46654669
}
46664670

4671+
/* call srandom based on some seed. NULL triggers the default behavior. */
4672+
staticvoid
4673+
set_random_seed(constchar*seed,constchar*origin)
4674+
{
4675+
/* srandom expects an unsigned int */
4676+
unsignedintiseed;
4677+
4678+
if (seed==NULL||strcmp(seed,"time")==0)
4679+
{
4680+
/* rely on current time */
4681+
instr_timenow;
4682+
INSTR_TIME_SET_CURRENT(now);
4683+
iseed= (unsignedint)INSTR_TIME_GET_MICROSEC(now);
4684+
}
4685+
elseif (strcmp(seed,"rand")==0)
4686+
{
4687+
/* use some "strong" random source */
4688+
if (!pg_strong_random(&iseed,sizeof(iseed)))
4689+
{
4690+
fprintf(stderr,"cannot seed random from a strong source\n");
4691+
exit(1);
4692+
}
4693+
}
4694+
else
4695+
{
4696+
/* parse seed unsigned int value */
4697+
chargarbage;
4698+
if (sscanf(seed,"%u%c",&iseed,&garbage)!=1)
4699+
{
4700+
fprintf(stderr,
4701+
"error while scanning '%s' from %s, expecting an unsigned integer, 'time' or 'rand'\n",
4702+
seed,origin);
4703+
exit(1);
4704+
}
4705+
}
4706+
4707+
if (seed!=NULL)
4708+
fprintf(stderr,"setting random seed to %u\n",iseed);
4709+
srandom(iseed);
4710+
/* no precision loss: 32 bit unsigned int cast to 64 bit int */
4711+
random_seed=iseed;
4712+
}
4713+
46674714

46684715
int
46694716
main(intargc,char**argv)
@@ -4706,6 +4753,7 @@ main(int argc, char **argv)
47064753
{"progress-timestamp",no_argument,NULL,6},
47074754
{"log-prefix",required_argument,NULL,7},
47084755
{"foreign-keys",no_argument,NULL,8},
4756+
{"random-seed",required_argument,NULL,9},
47094757
{NULL,0,NULL,0}
47104758
};
47114759

@@ -4774,6 +4822,9 @@ main(int argc, char **argv)
47744822
state= (CState*)pg_malloc(sizeof(CState));
47754823
memset(state,0,sizeof(CState));
47764824

4825+
/* set random seed early, because it may be used while parsing scripts. */
4826+
set_random_seed(getenv("PGBENCH_RANDOM_SEED"),"PGBENCH_RANDOM_SEED environment variable");
4827+
47774828
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)
47784829
{
47794830
char*script;
@@ -5046,6 +5097,10 @@ main(int argc, char **argv)
50465097
initialization_option_set= true;
50475098
foreign_keys= true;
50485099
break;
5100+
case9:/* random-seed */
5101+
benchmarking_option_set= true;
5102+
set_random_seed(optarg,"--random-seed option");
5103+
break;
50495104
default:
50505105
fprintf(stderr,_("Try \"%s --help\" for more information.\n"),progname);
50515106
exit(1);
@@ -5280,10 +5335,6 @@ main(int argc, char **argv)
52805335
exit(1);
52815336
}
52825337

5283-
/* set random seed */
5284-
INSTR_TIME_SET_CURRENT(start_time);
5285-
srandom((unsignedint)INSTR_TIME_GET_MICROSEC(start_time));
5286-
52875338
if (internal_script_used)
52885339
{
52895340
/*
@@ -5339,10 +5390,8 @@ main(int argc, char **argv)
53395390
if (lookupVariable(&state[0],"client_id")==NULL)
53405391
{
53415392
for (i=0;i<nclients;i++)
5342-
{
53435393
if (!putVariableInt(&state[i],"startup","client_id",i))
53445394
exit(1);
5345-
}
53465395
}
53475396

53485397
/* set default seed for hash functions */
@@ -5358,6 +5407,14 @@ main(int argc, char **argv)
53585407
exit(1);
53595408
}
53605409

5410+
/* set random seed unless overwritten */
5411+
if (lookupVariable(&state[0],"random_seed")==NULL)
5412+
{
5413+
for (i=0;i<nclients;i++)
5414+
if (!putVariableInt(&state[i],"startup","random_seed",random_seed))
5415+
exit(1);
5416+
}
5417+
53615418
if (!is_no_vacuum)
53625419
{
53635420
fprintf(stderr,"starting vacuum...");

‎src/bin/pgbench/t/001_pgbench_with_server.pl

Lines changed: 63 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -29,6 +29,12 @@ sub pgbench
2929
$filename =~s/\@\d+$//;
3030

3131
#push @filenames, $filename;
32+
# filenames are expected to be unique on a test
33+
if (-e$filename)
34+
{
35+
ok(0,"$filename must not already exists");
36+
unlink$filenameordie"cannot unlink$filename:$!";
37+
}
3238
append_to_file($filename,$$files{$fn});
3339
}
3440
}
@@ -210,14 +216,18 @@ sub pgbench
210216
} });
211217

212218
# test expressions
219+
# command 1..3 and 23 depend on random seed which is used to call srandom.
213220
pgbench(
214-
'-t 1 -Dfoo=-10.1 -Dbla=false -Di=+3 -Dminint=-9223372036854775808 -Dn=null -Dt=t -Df=of -Dd=1.0',
221+
'--random-seed=5432 -t 1 -Dfoo=-10.1 -Dbla=false -Di=+3 -Dminint=-9223372036854775808 -Dn=null -Dt=t -Df=of -Dd=1.0',
215222
0,
216223
[qr{type: .*/001_pgbench_expressions},qr{processed: 1/1} ],
217-
[qr{command=1.: int 1\d\b},
218-
qr{command=2.: int 1\d\d\b},
219-
qr{command=3.: int 1\d\d\d\b},
220-
qr{command=4.: int 4\b},
224+
[qr{setting random seed to 5432\b},
225+
# After explicit seeding, the four * random checks (1-3,20) should be
226+
# deterministic, but not necessarily portable.
227+
qr{command=1.: int 1\d\b},# uniform random: 12 on linux
228+
qr{command=2.: int 1\d\d\b},# exponential random: 106 on linux
229+
qr{command=3.: int 1\d\d\d\b},# gaussian random: 1462 on linux
230+
qr{command=4.: int 4\b},
221231
qr{command=5.: int 5\b},
222232
qr{command=6.: int 6\b},
223233
qr{command=7.: int 7\b},
@@ -230,7 +240,7 @@ sub pgbench
230240
qr{command=16.: double 16\b},
231241
qr{command=17.: double 17\b},
232242
qr{command=18.: int 9223372036854775807\b},
233-
qr{command=20.: int[1-9]\b},
243+
qr{command=20.: int\d\b},# zipfian random: 1 on linux
234244
qr{command=21.: double -27\b},
235245
qr{command=22.: double 1024\b},
236246
qr{command=23.: double 1\b},
@@ -270,6 +280,9 @@ sub pgbench
270280
qr{command=86.: int 86\b},
271281
qr{command=93.: int 93\b},
272282
qr{command=95.: int 0\b},
283+
qr{command=96.: int 1\b},# :scale
284+
qr{command=97.: int 0\b},# :client_id
285+
qr{command=98.: int 5432\b},# :random_seed
273286
],
274287
'pgbench expressions',
275288
{'001_pgbench_expressions'=>q{-- integer functions
@@ -390,8 +403,52 @@ sub pgbench
390403
\endif
391404
-- must be zero if false branches where skipped
392405
\set nope debug(:nope)
406+
-- check automatic variables
407+
\set sc debug(:scale)
408+
\set ci debug(:client_id)
409+
\set rs debug(:random_seed)
393410
} });
394411

412+
# random determinism when seeded
413+
$node->safe_psql('postgres',
414+
'CREATE UNLOGGED TABLE seeded_random(seed INT8 NOT NULL, rand TEXT NOT NULL, val INTEGER NOT NULL);');
415+
416+
# same value to check for determinism
417+
my$seed =int(rand(1000000000));
418+
formy$i (1, 2)
419+
{
420+
pgbench("--random-seed=$seed -t 1",
421+
0,
422+
[qr{processed: 1/1}],
423+
[qr{setting random seed to$seed\b}],
424+
"random seeded with$seed",
425+
{"001_pgbench_random_seed_$i"=>q{-- test random functions
426+
\set ur random(1000, 1999)
427+
\set er random_exponential(2000, 2999, 2.0)
428+
\set gr random_gaussian(3000, 3999, 3.0)
429+
\set zr random_zipfian(4000, 4999, 2.5)
430+
INSERT INTO seeded_random(seed, rand, val) VALUES
431+
(:random_seed, 'uniform', :ur),
432+
(:random_seed, 'exponential', :er),
433+
(:random_seed, 'gaussian', :gr),
434+
(:random_seed, 'zipfian', :zr);
435+
} });
436+
}
437+
438+
# check that all runs generated the same 4 values
439+
my ($ret,$out,$err) =
440+
$node->psql('postgres',
441+
'SELECT seed, rand, val, COUNT(*) FROM seeded_random GROUP BY seed, rand, val');
442+
443+
ok($ret == 0,"psql seeded_random count ok");
444+
ok($erreq'',"psql seeded_random count stderr is empty");
445+
ok($out =~/\b$seed\|uniform\|1\d\d\d\|2/,"psql seeded_random count uniform");
446+
ok($out =~/\b$seed\|exponential\|2\d\d\d\|2/,"psql seeded_random count exponential");
447+
ok($out =~/\b$seed\|gaussian\|3\d\d\d\|2/,"psql seeded_random count gaussian");
448+
ok($out =~/\b$seed\|zipfian\|4\d\d\d\|2/,"psql seeded_random count zipfian");
449+
450+
$node->safe_psql('postgres','DROP TABLE seeded_random;');
451+
395452
# backslash commands
396453
pgbench(
397454
'-t 1', 0,

‎src/bin/pgbench/t/002_pgbench_no_server.pl

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -110,6 +110,8 @@ sub pgbench_scripts
110110
['invalid init step','-i -I dta',
111111
[qr{unrecognized initialization step},
112112
qr{allowed steps are} ] ],
113+
['bad random seed','--random-seed=one',
114+
[qr{error while scanning 'one' from --random-seed option, expecting an unsigned integer} ] ],
113115

114116
# loging sub-options
115117
['sampling => log','--sampling-rate=0.01',

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