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From "Mingliang Liu (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9313) Possible NullPointerException in BlockManager if no excess replica can be chosen
Date Tue, 27 Oct 2015 01:01:32 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9313?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14975453#comment-14975453
] 

Mingliang Liu commented on HDFS-9313:
-------------------------------------

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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