Details
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Bug
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Status: Resolved
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Blocker
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Resolution: Fixed
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Impala 4.0.0
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None
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ghx-label-5
Description
When doing some TPC-DS benchmarking with mt_dop, we encountered intermittent performance regressions on short queries. Some query executions seem to be taking an extra 10 seconds in exec status reports due to delays in sending a cancel RPC. From the coordinator logs:
W0804 02:52:33.922088 108 rpcz_store.cc:253] Call impala.ControlService.CancelQueryFInstances from 127.0.0.1:46738 (request call id 3134) took 10007 ms (10 s). Client timeout 10000 ms (10 s)
W0804 02:52:33.922143 108 rpcz_store.cc:259] Trace:
0804 02:52:23.914291 (+ 0us) impala-service-pool.cc:170] Inserting onto call queue
0804 02:52:33.922079 (+10007788us) impala-service-pool.cc:255] Skipping call since client already timed out
0804 02:52:33.922086 (+ 7us) inbound_call.cc:162] Queueing failure response
Metrics: {}
I0804 02:52:33.922214 101 connection.cc:730] Got response to call id 3134 after client already timed out or cancelled
I0804 02:52:33.923286 20276 coordinator-backend-state.cc:889] query_id=f442e73a0d35c136:c9993d7700000000 target backend=xx.xx.xx.xx:27000: Sending CancelQueryFInstances rpc
The rpcz page also shows that some ReportExecStatus RPCs are taking 10 seconds:
"incoming_queue_time": "Count: 671901, min / max: 1000.000ns / 10s347ms, 25th %-ile: 12.000us, 50th %-ile: 18.000us, 75th %-ile: 28.000us, 90th %-ile: 67.000us, 95th %-ile: 456.000us, 99.9th %-ile: 10s133ms",
{
"method_name": "ReportExecStatus",
"handler_latency": "Count: 169653, min / max: 38.000us / 10s173ms, 25th %-ile: 9.024ms, 50th %-ile: 20.352ms, 75th %-ile: 35.840ms, 90th %-ile: 94.720ms, 95th %-ile: 177.152ms, 99.9th %-ile: 10s027ms",
"payload_size": "Count: 169653, min / max: 5.81 KB / 3.81 MB, 25th %-ile: 425.00 KB, 50th %-ile: 760.00 KB, 75th %-ile: 1.47 MB, 90th %-ile: 1.96 MB, 95th %-ile: 2.31 MB, 99.9th %-ile: 3.73 MB"
}]
IMPALA-6984 introduced a Coordinator::CancelBackends() call to Coordinator::HandleExecStateTransition() for the ExecState::RETURNED_RESULTS case:
if (new_state == ExecState::RETURNED_RESULTS) {
// Cancel all backends, but wait for the final status reports to be received so that
// we have a complete profile for this successful query.
CancelBackends(/*fire_and_forget=*/ false);
WaitForBackends();
} else {
CancelBackends(/*fire_and_forget=*/ true);
}
Removing this call eliminates the performance regression, so it will need more investigation.