Add --limit to limit latency under throttling
Under throttling, transactions are scheduled for execution at certain times.
Transactions may be far behind schedule and the system may catch up with the
load later. This option allows to change this behavior by skipping
transactions which are too far behind schedule, and count those as skipped.
The idea is to help simulate a latency-constrained environment such as a
database used by a web server.
Find attached a new version:
- fix dropped percent computation in the final report
- simplify progress report code
--
Fabien.
diff --git a/contrib/pgbench/pgbench.c b/contrib/pgbench/pgbench.c
index 2f7d80e..37a4a8f 100644
--- a/contrib/pgbench/pgbench.c
+++ b/contrib/pgbench/pgbench.c
@@ -141,6 +141,13 @@ double sample_rate = 0.0;
int64 throttle_delay = 0;
/*
+ * When under throttling, execution time slots which are more than
+ * this late (in us) are skipped, and the corresponding transaction
+ * will be counted as somehow aborted.
+ */
+int64 throttle_latency_limit = 0;
+
+/*
* tablespace selection
*/
char *tablespace = NULL;
@@ -238,6 +245,7 @@ typedef struct
int64 throttle_trigger; /* previous/next throttling (us) */
int64 throttle_lag; /* total transaction lag behind throttling */
int64 throttle_lag_max; /* max transaction lag */
+ int64 throttle_latency_skipped; /* lagging transactions skipped */
} TState;
#define INVALID_THREAD ((pthread_t) 0)
@@ -250,6 +258,7 @@ typedef struct
int64 sqlats;
int64 throttle_lag;
int64 throttle_lag_max;
+ int64 throttle_latency_skipped;
} TResult;
/*
@@ -367,6 +376,8 @@ usage(void)
" -f, --file=FILENAME read transaction script from FILENAME\n"
" -j, --jobs=NUM number of threads (default: 1)\n"
" -l, --log write transaction times to log file\n"
+ " -L, --limit=NUM under throttling (--rate), skip transactions that\n"
+ " far behind schedule in ms (default: do not skip)\n"
" -M, --protocol=simple|extended|prepared\n"
" protocol for submitting queries (default: simple)\n"
" -n, --no-vacuum do not run VACUUM before tests\n"
@@ -1016,6 +1027,24 @@ top:
thread->throttle_trigger += wait;
+ if (throttle_latency_limit)
+ {
+ instr_time now;
+ int64 now_us;
+ INSTR_TIME_SET_CURRENT(now);
+ now_us = INSTR_TIME_GET_MICROSEC(now);
+ while (thread->throttle_trigger < now_us - throttle_latency_limit)
+ {
+ /* if too far behind, this slot is skipped, and we
+ * iterate till the next nearly on time slot.
+ */
+ int64 wait = (int64) (throttle_delay *
+ 1.00055271703 * -log(getrand(thread, 1, 10000) / 10000.0));
+ thread->throttle_trigger += wait;
+ thread->throttle_latency_skipped ++;
+ }
+ }
+
st->until = thread->throttle_trigger;
st->sleeping = 1;
st->throttling = true;
@@ -2351,7 +2380,8 @@ printResults(int ttype, int64 normal_xacts, int nclients,
TState *threads, int nthreads,
instr_time total_time, instr_time conn_total_time,
int64 total_latencies, int64 total_sqlats,
- int64 throttle_lag, int64 throttle_lag_max)
+ int64 throttle_lag, int64 throttle_lag_max,
+ int64 throttle_latency_skipped)
{
double time_include,
tps_include,
@@ -2417,6 +2447,10 @@ printResults(int ttype, int64 normal_xacts, int nclients,
*/
printf("rate limit schedule lag: avg %.3f (max %.3f) ms\n",
0.001 * throttle_lag / normal_xacts, 0.001 * throttle_lag_max);
+ if (throttle_latency_limit)
+ printf("number of skipped transactions: " INT64_FORMAT " (%.3f %%)\n",
+ throttle_latency_skipped,
+ 100.0 * throttle_latency_skipped / (throttle_latency_skipped + normal_xacts));
}
printf("tps = %f (including connections establishing)\n", tps_include);
@@ -2505,6 +2539,7 @@ main(int argc, char **argv)
{"sampling-rate", required_argument, NULL, 4},
{"aggregate-interval", required_argument, NULL, 5},
{"rate", required_argument, NULL, 'R'},
+ {"limit", required_argument, NULL, 'L'},
{NULL, 0, NULL, 0}
};
@@ -2534,6 +2569,7 @@ main(int argc, char **argv)
int64 total_sqlats = 0;
int64 throttle_lag = 0;
int64 throttle_lag_max = 0;
+ int64 throttle_latency_skipped = 0;
int i;
@@ -2775,6 +2811,18 @@ main(int argc, char **argv)
throttle_delay = (int64) (1000000.0 / throttle_value);
}
break;
+ case 'L':
+ {
+ double limit_ms = atof(optarg);
+ if (limit_ms <= 0.0)
+ {
+ fprintf(stderr, "invalid latency limit: %s\n", optarg);
+ exit(1);
+ }
+ benchmarking_option_set = true;
+ throttle_latency_limit = (int64) (limit_ms * 1000);
+ }
+ break;
case 0:
/* This covers long options which take no argument. */
if (foreign_keys || unlogged_tables)
@@ -2895,6 +2943,12 @@ main(int argc, char **argv)
exit(1);
}
+ if (throttle_latency_limit != 0 && throttle_delay == 0)
+ {
+ fprintf(stderr, "latency limit (-L) can only be specified with throttling (-R)\n");
+ exit(1);
+ }
+
/*
* is_latencies only works with multiple threads in thread-based
* implementations, not fork-based ones, because it supposes that the
@@ -3070,6 +3124,7 @@ main(int argc, char **argv)
thread->random_state[0] = random();
thread->random_state[1] = random();
thread->random_state[2] = random();
+ thread->throttle_latency_skipped = 0;
if (is_latencies)
{
@@ -3144,6 +3199,7 @@ main(int argc, char **argv)
total_latencies += r->latencies;
total_sqlats += r->sqlats;
throttle_lag += r->throttle_lag;
+ throttle_latency_skipped += r->throttle_latency_skipped;
if (r->throttle_lag_max > throttle_lag_max)
throttle_lag_max = r->throttle_lag_max;
INSTR_TIME_ADD(conn_total_time, r->conn_time);
@@ -3166,7 +3222,7 @@ main(int argc, char **argv)
INSTR_TIME_SUBTRACT(total_time, start_time);
printResults(ttype, total_xacts, nclients, threads, nthreads,
total_time, conn_total_time, total_latencies, total_sqlats,
- throttle_lag, throttle_lag_max);
+ throttle_lag, throttle_lag_max, throttle_latency_skipped);
return 0;
}
@@ -3191,7 +3247,8 @@ threadRun(void *arg)
int64 last_count = 0,
last_lats = 0,
last_sqlats = 0,
- last_lags = 0;
+ last_lags = 0,
+ last_skipped = 0;
AggVals aggs;
@@ -3394,7 +3451,8 @@ threadRun(void *arg)
/* generate and show report */
int64 count = 0,
lats = 0,
- sqlats = 0;
+ sqlats = 0,
+ skipped = 0;
int64 lags = thread->throttle_lag;
int64 run = now - last_report;
double tps,
@@ -3417,23 +3475,24 @@ threadRun(void *arg)
sqlat = 1.0 * (sqlats - last_sqlats) / (count - last_count);
stdev = 0.001 * sqrt(sqlat - 1000000.0 * latency * latency);
lag = 0.001 * (lags - last_lags) / (count - last_count);
+ skipped = thread->throttle_latency_skipped - last_skipped;
+ fprintf(stderr,
+ "progress %d: %.1f s, %.1f tps, "
+ "lat %.3f ms stddev %.3f",
+ thread->tid, total_run, tps, latency, stdev);
if (throttle_delay)
- fprintf(stderr,
- "progress %d: %.1f s, %.1f tps, "
- "lat %.3f ms stddev %.3f, lag %.3f ms\n",
- thread->tid, total_run, tps, latency, stdev, lag);
- else
- fprintf(stderr,
- "progress %d: %.1f s, %.1f tps, "
- "lat %.3f ms stddev %.3f\n",
- thread->tid, total_run, tps, latency, stdev);
+ fprintf(stderr, ", lag %.3f ms", lag);
+ if (throttle_latency_limit)
+ fprintf(stderr, ", " INT64_FORMAT " skipped", skipped);
+ fprintf(stderr, "\n");
last_count = count;
last_lats = lats;
last_sqlats = sqlats;
last_lags = lags;
last_report = now;
+ last_skipped = thread->throttle_latency_skipped;
next_report += (int64) progress *1000000;
}
}
@@ -3452,7 +3511,8 @@ threadRun(void *arg)
int64 count = 0,
lats = 0,
sqlats = 0,
- lags = 0;
+ lags = 0,
+ skipped = 0;
int64 run = now - last_report;
double tps,
total_run,
@@ -3477,23 +3537,24 @@ threadRun(void *arg)
sqlat = 1.0 * (sqlats - last_sqlats) / (count - last_count);
stdev = 0.001 * sqrt(sqlat - 1000000.0 * latency * latency);
lag = 0.001 * (lags - last_lags) / (count - last_count);
+ skipped = thread->throttle_latency_skipped - last_skipped;
+ fprintf(stderr,
+ "progress: %.1f s, %.1f tps, "
+ "lat %.3f ms stddev %.3f",
+ total_run, tps, latency, stdev);
if (throttle_delay)
- fprintf(stderr,
- "progress: %.1f s, %.1f tps, "
- "lat %.3f ms stddev %.3f, lag %.3f ms\n",
- total_run, tps, latency, stdev, lag);
- else
- fprintf(stderr,
- "progress: %.1f s, %.1f tps, "
- "lat %.3f ms stddev %.3f\n",
- total_run, tps, latency, stdev);
+ fprintf(stderr, ", lag %.3f ms", lag);
+ if (throttle_latency_limit)
+ fprintf(stderr, ", " INT64_FORMAT " skipped", skipped);
+ fprintf(stderr, "\n");
last_count = count;
last_lats = lats;
last_sqlats = sqlats;
last_lags = lags;
last_report = now;
+ last_skipped = thread->throttle_latency_skipped;
next_report += (int64) progress *1000000;
}
}
@@ -3514,6 +3575,7 @@ done:
}
result->throttle_lag = thread->throttle_lag;
result->throttle_lag_max = thread->throttle_lag_max;
+ result->throttle_latency_skipped = thread->throttle_latency_skipped;
INSTR_TIME_SET_CURRENT(end);
INSTR_TIME_ACCUM_DIFF(result->conn_time, end, start);
if (logfile)
diff --git a/doc/src/sgml/pgbench.sgml b/doc/src/sgml/pgbench.sgml
index 23bfa9e..43a5582 100644
--- a/doc/src/sgml/pgbench.sgml
+++ b/doc/src/sgml/pgbench.sgml
@@ -345,6 +345,17 @@ pgbench <optional> <replaceable>options</> </optional> <replaceable>dbname</>
</varlistentry>
<varlistentry>
+ <term><option>-L</option> <replaceable>limit</></term>
+ <term><option>--limit=</option><replaceable>limit</></term>
+ <listitem>
+ <para>
+ Under throttling option <option>--rate=...</>, transactions behind schedule
+ by this number of ms will be skipped and counted as somehow aborted.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
<term><option>-M</option> <replaceable>querymode</></term>
<term><option>--protocol=</option><replaceable>querymode</></term>
<listitem>
@@ -437,7 +448,9 @@ pgbench <optional> <replaceable>options</> </optional> <replaceable>dbname</>
schedule moves forward based on when the client first started, not
when the previous transaction ended. That approach means that when
transactions go past their original scheduled end time, it is
- possible for later ones to catch up again.
+ possible for later ones to catch up again. It can be changed with
+ option <option>--limit</> which skips and counts transactions
+ late by more than this delay.
</para>
<para>
When throttling is active, the average and maximum transaction
--
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