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https://issues.apache.org/jira/browse/HDFS-12288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16122502#comment-16122502
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Hanisha Koneru commented on HDFS-12288:
---------------------------------------

Thanks for the fix, [~lukmajercak].
The patch LGTM. 
Just one NIT: In _TestNamenodeCapacityReport#testXceiverCountInternal_, can you 
please update the comment below.
{code}
        // the load for writers is 2 because both the write xceiver & packet
        // responder threads are counted in the load
        expectedTotalLoad += fileRepl;
        expectedInServiceLoad += fileRepl;
{code}

> Fix DataNode's xceiver count calculation
> ----------------------------------------
>
>                 Key: HDFS-12288
>                 URL: https://issues.apache.org/jira/browse/HDFS-12288
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode, hdfs
>            Reporter: Lukas Majercak
>            Assignee: Lukas Majercak
>         Attachments: HDFS-12288.001.patch
>
>
> The problem with the ThreadGroup.activeCount() method is that the method is 
> only a very rough estimate, and in reality returns the total number of 
> threads in the thread group as opposed to the threads actually running.
> In some DNs, we saw this to return 50~ for a long time, even though the 
> actual number of DataXceiver threads was next to none.
> This is a big issue as we use the xceiverCount to make decisions on the NN 
> for choosing replication source DN or returning DNs to clients for R/W.
> The plan is to reuse the DataNodeMetrics.dataNodeActiveXceiversCount value 
> which only accounts for actual number of DataXcevier threads currently 
> running and thus represents the load on the DN much better.



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