[jira] [Commented] (HDFS-8827) Erasure Coding: When namenode processes over replicated striped block, NPE will be occur in ReplicationMonitor

["Zhe Zhang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-8827?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14649980#comment-14649980 ] 

Zhe Zhang commented on HDFS-8827:
---------------------------------

Thanks for identifying the problem Fukudome-san! I took a quick look and the root cause doesn't seem straightforward. 

Do you mind creating a unit test generating the issue so we can all debug on the same basis? Thanks much!

> 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: 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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