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https://issues.apache.org/jira/browse/HDFS-4482?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Uma Maheswara Rao G updated HDFS-4482:
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Attachment: HDFS-4482.patch
Here is a simple patch to solve this problem.
> ReplicationMonitor thread can exit with NPE due to the race between delete
> and replication of same file.
> --------------------------------------------------------------------------------------------------------
>
> Key: HDFS-4482
> URL: https://issues.apache.org/jira/browse/HDFS-4482
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 2.0.1-alpha
> Reporter: Uma Maheswara Rao G
> Assignee: Uma Maheswara Rao G
> Priority: Blocker
> Attachments: HDFS-4482.patch
>
>
> Trace:
> {noformat}
> java.lang.NullPointerException
> at
> org.apache.hadoop.hdfs.server.namenode.FSDirectory.getFullPathName(FSDirectory.java:1442)
> at
> org.apache.hadoop.hdfs.server.namenode.INode.getFullPathName(INode.java:269)
> at
> org.apache.hadoop.hdfs.server.namenode.INodeFile.getName(INodeFile.java:163)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicy.chooseTarget(BlockPlacementPolicy.java:131)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeReplicationWorkForBlocks(BlockManager.java:1157)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeReplicationWork(BlockManager.java:1063)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeDatanodeWork(BlockManager.java:3085)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$ReplicationMonitor.run(BlockManager.java:3047)
> at java.lang.Thread.run(Thread.java:619)
> {noformat}
> What I am seeing here is:
> 1) create a file and write with 2 DNS
> 2) Close the file.
> 3) Kill one DN
> 4) Let replication start.
> Info:
> {code}
> // choose replication targets: NOT HOLDING THE GLOBAL LOCK
> // It is costly to extract the filename for which chooseTargets is
> called,
> // so for now we pass in the block collection itself.
> rw.targets = blockplacement.chooseTarget(rw.bc,
> rw.additionalReplRequired, rw.srcNode, rw.liveReplicaNodes,
> excludedNodes, rw.block.getNumBytes());{code}
> Here we are choosing target outside the global lock. Inside we will try to
> get the src path from blockCollection(nothing but INodeFile here).
> see the code for FSDirectory#getFullPathName
> Here it is incrementing the depth until it has parent. and Later it will
> iterate and access parent again in next loop.
> 5) before going to secnd loop in FSDirectory#getFullPathName, if file is
> deleted by client then that parent would have been set as null. So, here
> accessing the parent can cause NPE because it is not under lock.
> [~brahmareddy] reported this issue.
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