Hello Yugo-san,
For example, when I usee a large rate (-R) for throttling and a
small latency limit (-L) values with a duration (-T), pbbench
got stuck.
$ pgbench -T 5 -R 100000000 -L 1;
Indeed, it does not get out of the catchup loop for a long time because
even scheduling takes more time than the expected transaction time!
I think it is better to check the timer expiration even in the loop
of transaction skips and to finish pgbnech successfully because we
should correcly repport how many transactions are proccessed and
skipped also in this case, and getting stuck would not be good
anyway.
I attached a patch for this fix.
The patch mostly works for me, and I agree that the bench should not be in
a loop on any parameters, even when "crazy" parameters are given…
However I'm not sure this is the right way to handle this issue.
The catch-up loop can be dropped and the automaton can loop over itself to
reschedule. Doing that as the attached fixes this issue and also makes
progress reporting work proprely in more cases, and reduces the number of
lines of code. I did not add a test case because time sensitive tests have
been removed (which is too bad, IMHO).
--
Fabien.
diff --git a/src/bin/pgbench/pgbench.c b/src/bin/pgbench/pgbench.c
index d7479925cb..fe75533e3e 100644
--- a/src/bin/pgbench/pgbench.c
+++ b/src/bin/pgbench/pgbench.c
@@ -3223,31 +3223,30 @@ advanceConnectionState(TState *thread, CState *st, StatsData *agg)
/*
* If --latency-limit is used, and this slot is already late
* so that the transaction will miss the latency limit even if
- * it completed immediately, skip this time slot and schedule
- * to continue running on the next slot that isn't late yet.
- * But don't iterate beyond the -t limit, if one is given.
+ * it completed immediately, skip this time slot and loop to
+ * reschedule.
*/
if (latency_limit)
{
pg_time_now_lazy(&now);
- while (thread->throttle_trigger < now - latency_limit &&
- (nxacts <= 0 || st->cnt < nxacts))
+ if (thread->throttle_trigger < now - latency_limit)
{
processXactStats(thread, st, &now, true, agg);
- /* next rendez-vous */
- thread->throttle_trigger +=
- getPoissonRand(&thread->ts_throttle_rs, throttle_delay);
- st->txn_scheduled = thread->throttle_trigger;
- }
- /*
- * stop client if -t was exceeded in the previous skip
- * loop
- */
- if (nxacts > 0 && st->cnt >= nxacts)
- {
- st->state = CSTATE_FINISHED;
+ /* stop client if -T/-t was exceeded. */
+ if (timer_exceeded || (nxacts > 0 && st->cnt >= nxacts))
+ /*
+ * For very unrealistic rates under -T, some skipped
+ * transactions are not counted because the catchup
+ * loop is not fast enough just to do the scheduling
+ * and counting at the expected speed.
+ *
+ * We do not bother with such a degenerate case.
+ */
+ st->state = CSTATE_FINISHED;
+
+ /* otherwise loop over PREPARE_THROTTLE */
break;
}
}
