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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