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https://issues.apache.org/jira/browse/HDFS-8827?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jing Zhao updated HDFS-8827:
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    Attachment: HDFS-8827.2.patch

Thanks [~tfukudom] for working on this! I agree with Walter that for the unit 
test, the NPE is more like caused by the testing code. The .2 patch writes the 
real data instead of using {{createStripedFile}}, but it exposes some other 
bugs in the current writing code path so I have to change the block size from 1 
cell to 4 cells. In the meanwhile the test passed with the change. So the NPE 
you saw in the system test may be caused by some other issue. I will dig 
further into that.

> Erasure Coding: When namenode processes over replicated striped block, NPE 
> will be occur in ReplicationMonitor
> --------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-8827
>                 URL: https://issues.apache.org/jira/browse/HDFS-8827
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Takuya Fukudome
>            Assignee: Takuya Fukudome
>         Attachments: HDFS-8827.1.patch, HDFS-8827.2.patch, 
> processing-over-replica-npe.log
>
>
> In our test cluster, when namenode processed over replicated striped blocks, 
> null pointer exception(NPE) occurred. This happened under below situation: 1) 
> some datanodes shutdown. 2) namenode recovers block group which lost internal 
> blocks. 3) restart the stopped datanodes. 4) namenode processes over 
> replicated striped blocks. 5) NPE occurs
> I think BlockPlacementPolicyDefault#chooseReplicaToDelete will return null in 
> this situation which causes this NPE problem.



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