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https://issues.apache.org/jira/browse/HDFS-12288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16124333#comment-16124333
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Lukas Majercak edited comment on HDFS-12288 at 8/12/17 12:19 AM:
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It does not represent number of active threads in the process either. I am
currently looking at a DataNode that shows:
{{xceiverCount}} = 15
and JVM metrics show:
"ThreadsRunnable" : 64,
"ThreadsBlocked" : 0,
"ThreadsWaiting" : 13,
"ThreadsTimedWaiting" : 54,
"ThreadsTerminated" : 0,
was (Author: lukmajercak):
It does not represent number of active threads either. I am currently looking
at a DataNode that shows:
{{xceiverCount}} = 15
and JVM metrics show:
"ThreadsRunnable" : 64,
"ThreadsBlocked" : 0,
"ThreadsWaiting" : 13,
"ThreadsTimedWaiting" : 54,
"ThreadsTerminated" : 0,
> 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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