Ming Ma created HDFS-6425:
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             Summary: reset postponedMisreplicatedBlocks and 
postponedMisreplicatedBlocksCount when NN becomes active
                 Key: HDFS-6425
                 URL: https://issues.apache.org/jira/browse/HDFS-6425
             Project: Hadoop HDFS
          Issue Type: Bug
            Reporter: Ming Ma
            Assignee: Ming Ma


Sometimes we have large number of over replicates when NN fails over. When the 
new active NN took over, over replicated blocks will be put to 
postponedMisreplicatedBlocks until all DNs for that block aren't stale anymore.

We have a case where NNs flip flop. Before postponedMisreplicatedBlocks became 
empty, NN fail over again and again. So postponedMisreplicatedBlocks just kept 
increasing until the cluster is stable. 

In addition, large postponedMisreplicatedBlocks could make 
rescanPostponedMisreplicatedBlocks slow. rescanPostponedMisreplicatedBlocks 
takes write lock. So it could slow down the block report processing.



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