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https://issues.apache.org/jira/browse/HDFS-9313?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15038479#comment-15038479
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Xiao Chen commented on HDFS-9313:
---------------------------------
As [discussed in
HDFS-8647|https://issues.apache.org/jira/browse/HDFS-8647?focusedCommentId=15032747&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15032747],
I'm providing branch2.6/2.7 patch for this JIRA.
Cherry-picking from branch2, the backport was clean. But I had to fix a compile
error about {{HdfsServerConstants}} due to file change. Additionally I removed
the logging change, in order for the code to run. (Otherwise error at run time:
(java.lang.ClassCastException: org.slf4j.impl.Log4jLoggerAdapter cannot be cast
to org.apache.commons.logging.impl.Log4JLogger)).
Locally tested both patches compile and passes TestReplicationPolicy.
> 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
> Fix For: 2.8.0
>
> Attachments: HDFS-9313-2.patch, HDFS-9313.branch26.patch,
> HDFS-9313.branch27.patch, 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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