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https://issues.apache.org/jira/browse/HADOOP-12908?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15800182#comment-15800182
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John Zhuge commented on HADOOP-12908:
-------------------------------------
{{JvmMetrics}} is not a singleton in MiniDFSCluster, {{NameNodeMetrics}} and
{{DataNodeMetrics}} contain different instances.
> Make JvmPauseMonitor a singleton
> --------------------------------
>
> Key: HADOOP-12908
> URL: https://issues.apache.org/jira/browse/HADOOP-12908
> Project: Hadoop Common
> Issue Type: Improvement
> Affects Versions: 2.7.2
> Reporter: John Zhuge
> Assignee: John Zhuge
> Priority: Minor
> Attachments: HADOOP-12908-001.patch, HADOOP-12908-002.patch,
> HADOOP-12908-003.patch
>
>
> Make JvmPauseMonitor a singleton just as JvmMetrics because there is no use
> case to run multiple instances per JVM. {{TestMetrics$setPauseMonitor}}
> becomes obsolete. Initialization code for various components can be
> simplified.
> For example, this code segment
> {code}
> pauseMonitor = new JvmPauseMonitor();
> addService(pauseMonitor);
> jm.setPauseMonitor(pauseMonitor);
> {code}
> can be replaced with
> {code}
> addService(JvmPauseMonitor.getInstance());
> {code}
> And this code segment
> {code}
> pauseMonitor = new JvmPauseMonitor();
> pauseMonitor.init(config);
> pauseMonitor.start();
> metrics.getJvmMetrics().setPauseMonitor(pauseMonitor);
> {code}
> can be replaced with
> {code}
> pauseMonitor = JvmPauseMonitor.getInstance();
> pauseMonitor.init(config);
> pauseMonitor.start();
> {code}
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