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From "Uma Maheswara Rao G (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4482) ReplicationMonitor thread can exit with NPE due to the race between delete and replication of same file.
Date Tue, 12 Feb 2013 10:35:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4482?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13576530#comment-13576530

Uma Maheswara Rao G commented on HDFS-4482:

@Kihwal, Agreed. Current implementation of default placement policy not using src path any
where. I am not sure about the motivation in that API design, I think one point may be, that
users may want to use that src path in their custom placement policy. Since that is exposed
placemnet policy, user can write their own policy and plugin. In their implementation they
might use that path for some purpose. So, I don't think, we can change that anyway now.
> 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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