Ming Ma created HDFS-9313:
-----------------------------
Summary: 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
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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