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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1486) ReplicationMonitor thread goes away
Date Tue, 26 Jun 2007 18:07:27 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12508264

Doug Cutting commented on HADOOP-1486:

> whether to have a monitoring daemon that restarts namenode automatically

It seems safe to restart the namenode in this case.  I'd simply add a loop to NameNode.main()
that creates and starts a new NameNode when the existing namenode exits unexpectedly.  We
should only restart if it's stopping due to an error, and not due to an explicit call to stop().
 So perhaps NameNode#join() could return a boolean indicating whether it's exiting normally
or should be restarted, and the catch in the ReplicationMonitor should call a NameNode method
to trigger that kind of exit.  Does this sound workable?

> ReplicationMonitor thread goes away 
> ------------------------------------
>                 Key: HADOOP-1486
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1486
>             Project: Hadoop
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.12.3
>            Reporter: Koji Noguchi
>            Assignee: dhruba borthakur
>            Priority: Blocker
>             Fix For: 0.14.0
>         Attachments: catchThrowable2.patch
> Saw many over/under replicated blocks in fsck output.
> .out file showed
> Exception in thread "org.apache.hadoop.dfs.FSNamesystem$ReplicationMonitor@2785982c"
java.lang.IllegalArgumentException: Unexpected non-existing data node: /
>   at org.apache.hadoop.net.NetworkTopology.checkArgument(NetworkTopology.java:379)
>   at org.apache.hadoop.net.NetworkTopology.isOnSameRack(NetworkTopology.java:424)
>   at org.apache.hadoop.dfs.FSNamesystem$ReplicationTargetChooser.chooseTarget(FSNamesystem.java:2853)
>   at org.apache.hadoop.dfs.FSNamesystem$ReplicationTargetChooser.chooseTarget(FSNamesystem.java:2816)
>   at org.apache.hadoop.dfs.FSNamesystem.pendingTransfers(FSNamesystem.java:2658)
>   at org.apache.hadoop.dfs.FSNamesystem.computeDatanodeWork(FSNamesystem.java:1774)
>   at org.apache.hadoop.dfs.FSNamesystem$ReplicationMonitor.run(FSNamesystem.java:1723)
>   at java.lang.Thread.run(Thread.java:619)
> (same as HADOOP-1232)
> And, jstack showed no ReplicationMonitor thread.

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