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From "Lukas Majercak (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HDFS-12288) Fix DataNode's xceiver count calculation
Date Sat, 12 Aug 2017 00:20:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-12288?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16124333#comment-16124333
] 

Lukas Majercak edited comment on HDFS-12288 at 8/12/17 12:19 AM:
-----------------------------------------------------------------

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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