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From "Ming Ma (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-5757) Decommisson lots of nodes at the same time could slow down NN
Date Fri, 10 Jan 2014 19:51:50 GMT
Ming Ma created HDFS-5757:
-----------------------------

             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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