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From "Rushabh S Shah (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-12288) Fix DataNode's xceiver count calculation
Date Sat, 12 Aug 2017 00:15:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-12288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16124324#comment-16124324
] 

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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