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https://issues.apache.org/jira/browse/HDFS-8827?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14660542#comment-14660542
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Jing Zhao commented on HDFS-8827:
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Thanks [~tfukudom] for further investigation and thanks Walter for the fix! The
patch looks good to me. One minor:
{code}
// the number of target left replicas equals to the of number of the found
// indices, since we want every index has one replica left.
int numOfTarget = found.cardinality();
int numToDelete = nonExcess.size() - numOfTarget;
// the number of expected left replicas in nonExcess. It doesn't include the
// replicas belonging to the blockGroup but not in nonExcess.
int numOfLeft = nonExcess.size() - numToDelete;
{code}
Here the numOfLeft is actually numOfTarget, also the javadoc needs to be
polished.
> 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-HDFS-7285.04.patch, 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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