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https://issues.apache.org/jira/browse/HADOOP-16850?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17036717#comment-17036717
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Akira Ajisaka commented on HADOOP-16850:
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The test result is as follows on my virtual machine (CentOS 7):
{noformat}
#Threads=100, ThreadMXBean=346175 ns, ThreadGroup=77695 ns, ratio: 4
#Threads=200, ThreadMXBean=1018005 ns, ThreadGroup=76144 ns, ratio: 13
#Threads=500, ThreadMXBean=4421633 ns, ThreadGroup=185276 ns, ratio: 23
#Threads=1000, ThreadMXBean=15505098 ns, ThreadGroup=221509 ns, ratio: 69
#Threads=2000, ThreadMXBean=63139330 ns, ThreadGroup=399617 ns, ratio: 157
#Threads=3000, ThreadMXBean=161553471 ns, ThreadGroup=559847 ns, ratio: 288
{noformat}
> Support getting thread info from thread group for JvmMetrics to improve the
> performance
> ---------------------------------------------------------------------------------------
>
> Key: HADOOP-16850
> URL: https://issues.apache.org/jira/browse/HADOOP-16850
> Project: Hadoop Common
> Issue Type: Improvement
> Components: metrics
> Affects Versions: 2.8.6, 2.9.3, 3.1.4, 3.2.2, 2.10.1, 3.3.1
> Reporter: Tao Yang
> Assignee: Tao Yang
> Priority: Major
> Attachments: HADOOP-16850.001.patch, HADOOP-16850.002.patch
>
>
> Recently we found jmx request taken almost 5s+ to be done when there were 1w+
> threads in a stressed datanode process, meanwhile other http requests were
> blocked and some disk operations were affected (we can see many "Slow
> manageWriterOsCache" messages in DN log, and these messages were hard to be
> seen again after we stopped sending jxm requests)
> The excessive time is spent in getting thread info via ThreadMXBean inside
> which ThreadImpl#getThreadInfo native method is called, the time complexity
> of ThreadImpl#getThreadInfo is O(n*n) according to
> [JDK-8185005|https://bugs.openjdk.java.net/browse/JDK-8185005] and it holds
> global thread lock and prevents creation or termination of threads.
> To improve this, I propose to support getting thread info from thread group
> which will improve a lot by default, also support using original approach
> when "-Dhadoop.metrics.jvm.use-thread-mxbean=true" is configured in the
> startup command.
> An example of performance tests between these two approaches is as follows:
> {noformat}
> #Threads=100, ThreadMXBean=382372 ns, ThreadGroup=72046 ns, ratio: 5
> #Threads=200, ThreadMXBean=776619 ns, ThreadGroup=83875 ns, ratio: 9
> #Threads=500, ThreadMXBean=3392954 ns, ThreadGroup=216269 ns, ratio: 15
> #Threads=1000, ThreadMXBean=9475768 ns, ThreadGroup=220447 ns, ratio: 42
> #Threads=2000, ThreadMXBean=53833729 ns, ThreadGroup=579608 ns, ratio: 92
> #Threads=3000, ThreadMXBean=196829971 ns, ThreadGroup=1157670 ns, ratio: 170
> {noformat}
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