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https://issues.apache.org/jira/browse/HDFS-12288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16124324#comment-16124324
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Rushabh S Shah commented on HDFS-12288:
---------------------------------------
{quote}
I believe, that for the correctness of the metrics, we should avoid doing this
as it just introduces confusion as to what does the xciever count actually mean.
{quote}
{code:title=DataNode.java|borderStyle=solid}
/** Number of concurrent xceivers per node. */
@Override // DataNodeMXBean
public int getXceiverCount() {
return threadGroup == null ? 0 : threadGroup.activeCount();
}
{code}
All I can say is its a poorly named method.
What it actually represents is number of active threads in the datanode process.
So this patch is replacing {{number of active threads}} with just the {{number
of xceiver threads}}.
> 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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