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https://issues.apache.org/jira/browse/HADOOP-1092?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12479411
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dhruba borthakur commented on HADOOP-1092:
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A Datanode times-out and is declared dead by the Namenode. The Namenode invokes
removeDatanode. This Datanode has a block that has only one replica.
Inside removeStoredBlock(), we remove this block from the blocksMap and then
call neededReplication. update(block, -1, 0). Inside update(), we call
blocksMap.get() and we fail to find the block becaase we have just removed it.
Hence the null-pointer exception.
> NullPointerException in HeartbeatMonitor thread
> -----------------------------------------------
>
> Key: HADOOP-1092
> URL: https://issues.apache.org/jira/browse/HADOOP-1092
> Project: Hadoop
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.12.0
> Reporter: Nigel Daley
> Priority: Blocker
> Fix For: 0.12.1
>
>
> Running NNBench with latest trunk, I saw this NPE in the Namenode log:
> Exception in thread "[EMAIL PROTECTED]" java.lang.NullPointerException
> at
> org.apache.hadoop.dfs.FSNamesystem.countContainingNodes(FSNamesystem.java:2506)
> at org.apache.hadoop.dfs.FSNamesystem.access$000(FSNamesystem.java:52)
> at
> org.apache.hadoop.dfs.FSNamesystem$UnderReplicationBlocks.update(FSNamesystem.java:456)
> at
> org.apache.hadoop.dfs.FSNamesystem.removeStoredBlock(FSNamesystem.java:2242)
> at
> org.apache.hadoop.dfs.FSNamesystem.removeDatanode(FSNamesystem.java:1876)
> at
> org.apache.hadoop.dfs.FSNamesystem.heartbeatCheck(FSNamesystem.java:1958)
> at
> org.apache.hadoop.dfs.FSNamesystem$HeartbeatMonitor.run(FSNamesystem.java:1698)
> at java.lang.Thread.run(Thread.java:619)
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