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https://issues.apache.org/jira/browse/HDFS-11180?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15707967#comment-15707967
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Akira Ajisaka commented on HDFS-11180:
--------------------------------------

{quote}
bq. NameNode holds a lock of FSEditLog and requires a lock of MetricsSystemImpl 
when registering IPCLoggerChannel metrics.
It looks like this deadlock can happen only when the QJM is used.
{quote}
In addition, this deadlock can happen only when there is at least one metrics 
sink registered to MetricsSystem. If there is no metrics sink, 
MetricsSystemImpl.sampleMetrics can not be called.

> Intermittent deadlock in NameNode when failover happens.
> --------------------------------------------------------
>
>                 Key: HDFS-11180
>                 URL: https://issues.apache.org/jira/browse/HDFS-11180
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 2.6.0
>            Reporter: Abhishek Modi
>            Assignee: Akira Ajisaka
>            Priority: Blocker
>              Labels: high-availability
>         Attachments: HDFS-11180.00.patch, HDFS-11180.01.patch, 
> HDFS-11180.02.patch, HDFS-11180.03.patch, HDFS-11180.04.patch, jstack.log
>
>
> It is happening due to metrics getting updated at the same time when failover 
> is happening. Please find attached jstack at that point of time.



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