[jira] [Created] (HDFS-5757) Decommisson lots of nodes at the same time could slow down NN

["Ming Ma (JIRA)" <ji...@apache.org>]

Ming Ma created HDFS-5757:
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             Summary: Decommisson lots of nodes at the same time could slow down NN
                 Key: HDFS-5757
                 URL: https://issues.apache.org/jira/browse/HDFS-5757
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: namenode
            Reporter: Ming Ma


Sometimes we need to decomm a whole rack of nodes at the same time. When the decomm is in process; NN is slow.

The reason is when DecommissionManager checks the decomm status, it acquires namesystem's writer lock and iterates through all DNs; for each DN that is in decommissioning state, it check if replication is done for all the blocks on the machine via blockManager.isReplicationInProgress; for large cluster; the number of blocks on the machine could be big.

The fix could be to have DecommissionManager check for several decomm-in-progress nodes each time it aquires namesystem's writer lock.



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