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https://issues.apache.org/jira/browse/HDFS-12638?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16203577#comment-16203577
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Daryn Sharp commented on HDFS-12638:
------------------------------------
There's 2 likely scenarios:
* The block is added to the blocks map with an unlinked inode not in the inode
map. The only way to add a block to the map is via
{{BlockManager#addBlockCollection}}. Truncate, like add block, does this but
it should not have been able to resolve the inode if it's unlinked and I don't
immediately see locking issues.
* The lease manager encountered an error and removed the inode but left the
blocks intact. Look for log warn of "Removing lease with an invalid path"
because the lease manager catches IOEs and just removes the inode anyway which
can leave the blocks map in an inconsistent state. Very bad.
> NameNode exits due to ReplicationMonitor thread received Runtime exception in
> ReplicationWork#chooseTargets
> -----------------------------------------------------------------------------------------------------------
>
> Key: HDFS-12638
> URL: https://issues.apache.org/jira/browse/HDFS-12638
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs
> Affects Versions: 2.8.2
> Reporter: Jiandan Yang
>
> Active NamNode exit due to NPE, I can confirm that the BlockCollection passed
> in when creating ReplicationWork is null, but I do not know why
> BlockCollection is null, By view history I found
> [HDFS-9754|https://issues.apache.org/jira/browse/HDFS-9754] remove judging
> whether BlockCollection is null.
> NN logs are as following:
> {code:java}
> 2017-10-11 16:29:06,161 ERROR [ReplicationMonitor]
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager:
> ReplicationMonitor thread received Runtime exception.
> java.lang.NullPointerException
> at
> org.apache.hadoop.hdfs.server.blockmanagement.ReplicationWork.chooseTargets(ReplicationWork.java:55)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeReplicationWorkForBlocks(BlockManager.java:1532)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeReplicationWork(BlockManager.java:1491)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.computeDatanodeWork(BlockManager.java:3792)
> at
> org.apache.hadoop.hdfs.server.blockmanagement.BlockManager$ReplicationMonitor.run(BlockManager.java:3744)
> at java.lang.Thread.run(Thread.java:834)
> {code}
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