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https://issues.apache.org/jira/browse/HDFS-8211?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14509357#comment-14509357
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Anu Engineer commented on HDFS-8211:
------------------------------------

I will make the test simpler, thanx for the pointers

bq. The test case seems to pass without the code change.

The reason being that all the functions of DataNode are private and it is not 
possible to trigger the error path from outside. The checkuuid call would write 
the UUID to storage variable and then on the connection complete it gets copied 
to id. so the fix is just to read from the storage variable rather than id 
since both f them point to same values.

At this point the test simply verifies that new code change that is made does 
not lead to regressions, it does *not* test for the initial race condition


> DataNode UUID is always null in the JMX counter
> -----------------------------------------------
>
>                 Key: HDFS-8211
>                 URL: https://issues.apache.org/jira/browse/HDFS-8211
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: HDFS
>    Affects Versions: 2.7.0
>            Reporter: Anu Engineer
>            Assignee: Anu Engineer
>            Priority: Minor
>         Attachments: hdfs-8211.001.patch
>
>
> The DataNode JMX counters are tagged with DataNode UUID, but it always gets a 
> null value instead of the UUID.
> {code}
> Hadoop:service=DataNode,name=FSDatasetState*-null*.
> {code}
> This null is supposed be the datanode UUID.



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