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https://issues.apache.org/jira/browse/HDFS-8827?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14660029#comment-14660029
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Walter Su commented on HDFS-8827:
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When I said "a missing internalBlk" and "a redundant internalBlk". I mean they
should happen at the same time. Even though very unlikely.
We lost a blk with idx=1, how could ReplicationMonitor replicate a idx=3 to
make it redundant? Maybe A dead DN comes back before ReplicationMonitor finds
out.
> 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, HDFS-8827.3.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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