Lukas Majercak created HDFS-12288:
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Summary: Change DN 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
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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