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https://issues.apache.org/jira/browse/HDFS-9313?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14975453#comment-14975453
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Mingliang Liu commented on HDFS-9313:
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Thanks for filing and working on this, [~mingma]. I think the patch makes sense
to me. The warning is much better than a NPE.
{code}
+ // no replica can't be chosen as the excessive replica as
{code}
Do you mean "no replica *can* be chosen as the excessive replica as"?
> Possible NullPointerException in BlockManager if no excess replica can be
> chosen
> --------------------------------------------------------------------------------
>
> Key: HDFS-9313
> URL: https://issues.apache.org/jira/browse/HDFS-9313
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Ming Ma
> Assignee: Ming Ma
> Attachments: HDFS-9313.patch
>
>
> HDFS-8647 makes it easier to reason about various block placement scenarios.
> Here is one possible case where BlockManager won't be able to find the excess
> replica to delete: when storage policy changes around the same time balancer
> moves the block. When this happens, it will cause NullPointerException.
> {noformat}
> java.lang.NullPointerException
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy.adjustSetsWithChosenReplica(BlockPlacementPolicy.java:156)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseReplicasToDelete(BlockPlacementPolicyDefault.java:978)
> {noformat}
> Note that it isn't found in any production clusters. Instead, it is found
> from new unit tests. In addition, the issue has been there before HDFS-8647.
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