odraese commented on a change in pull request #633: HIVE-21740: Collect LLAP 
execution latency metrics
URL: https://github.com/apache/hive/pull/633#discussion_r285714898
 
 

 ##########
 File path: 
llap-tez/src/java/org/apache/hadoop/hive/llap/tezplugins/metrics/LlapTaskSchedulerMetrics.java
 ##########
 @@ -276,6 +302,43 @@ private void getTaskSchedulerStats(MetricsRecordBuilder 
rb) {
         .addCounter(SchedulerPendingPreemptionTaskCount, 
pendingPreemptionTasksCount.value())
         .addCounter(SchedulerPreemptedTaskCount, preemptedTasksCount.value())
         .addCounter(SchedulerCompletedDagCount, completedDagcount.value());
+    daemonTaskLatency.forEach((k, v) -> rb.addGauge(v, v.getMean()));
+  }
+
+  static class DaemonLatencyMetric implements MetricsInfo {
+    private String name;
+    private ExponentiallyDecayingReservoir reservoir;
 
 Review comment:
   What is the benefit of using am exponential decay here, vs. simple sliding 
window (i.e. guava stats)? Specifically with the low amount of entries (right 
now 1028), a few more recent task execution times can have a huge impact on 
what we believe is the node's average over a longer period of time. The whole 
idea of using the average here is to smooth out the task execution times across 
a larger amount of tasks. I have the fear, that the exponential decay is 
contradicting this by giving few, very recent values, a high impact.

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