[jira] [Updated] (HDFS-12288) Fix DataNode's xceiver count calculation

["Wei-Chiu Chuang (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-12288?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Wei-Chiu Chuang updated HDFS-12288:
-----------------------------------
    Fix Version/s: 3.3.1

> 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: Lisheng Sun
>            Priority: Major
>             Fix For: 3.3.1, 3.4.0
>
>         Attachments: HDFS-12288.001.patch, HDFS-12288.002.patch, HDFS-12288.003.patch, HDFS-12288.004.patch, HDFS-12288.005.patch, HDFS-12288.006.patch, HDFS-12288.007.patch, HDFS-12288.008.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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