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https://issues.apache.org/jira/browse/HDFS-12288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16124597#comment-16124597
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Íñigo Goiri commented on HDFS-12288:
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Thanks [~shahrs87], I think that makes sense.
Just to confirm, the proposal would be:
# Change the JMX method {{DataNode#getXceiverCount()}} to report the right
xceiver count as [~lukmajercak] proposes.
# Add a new method called {{DataNode#getActiveNumberOfThreads()}} which has the
old behavior from {{DataNode#getXceiverCount()}} (using
{{threadGroup.activeCount()}}).
# Use this new {{getActiveNumberOfThreads()}} for the configuration check and
so on.
I like that solution.
[~lukmajercak], do you mind posting a patch with that?
> 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, HDFS-12288.002.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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