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https://issues.apache.org/jira/browse/AMBARI-24244?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Hari Sekhon updated AMBARI-24244:
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Summary: Grafana HBase GC Time graph wrong / misleading - hiding large GC
pauses ~ 2 dozen secs! (was: Grafana HBase GC Time graph wrong / misleading -
hiding large GC pauses)
> Grafana HBase GC Time graph wrong / misleading - hiding large GC pauses ~ 2
> dozen secs!
> ---------------------------------------------------------------------------------------
>
> Key: AMBARI-24244
> URL: https://issues.apache.org/jira/browse/AMBARI-24244
> Project: Ambari
> Issue Type: Bug
> Components: ambari-metrics, metrics
> Affects Versions: 2.5.2
> Reporter: Hari Sekhon
> Priority: Major
>
> Ambari's in-built Grafana graph for "JVM GC Times" graph in the HBase -
> RegionServers dashboard is very wrong and doesn't reflect the times I've
> grepped across HBase RegionServer logs for util.JvmPauseMonitor.
> I've inherited a very heavily loaded HBase + OpenTSDB cluster where there are
> RegionServer losses occurring due to GCs around 30 seconds(!) causing ZK +
> HMaster to declare them dead. The Grafana graphs show peaks around 70ms due
> to averaging the GC time spent over all seconds, which smooths out the peaks
> so as to not show any problem. If you are going to use GCTimeMillis then I
> believe you need to divide by GCCount.
> Otherwise I believe this is actually the wrong metric to be watching and
> instead the following metric from HBase JMX should be monitored with a value
> of last. This does show the significant GC time spent:
> {code:java}
> java.lang:type=GarbageCollector,name=G1 Old Generation -> LastGcInfo ->
> duration{code}
> Obviously make it search for a regex to match whichever garbage collector you
> are using, whether G1 or CMS etc:
> {code:java}
> java.lang:type=GarbageCollector,name=.*Old Gen.* -> LastGcInfo ->
> duration{code}
> Right now the GC Times graph is worse than useless, it's misleading as it
> implies there are no GC issues when there are actually very large very severe
> GC issues on this cluster.
> This is a vanilla Ambari deployed Grafana with Ambari Metrics.
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