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https://issues.apache.org/jira/browse/MAPREDUCE-935?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12748984#action_12748984
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Steve Loughran commented on MAPREDUCE-935:
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Looking at the thread dump, it also looks like the exponential backoff feature
in the {{Client.handleConnectFailure()}} is interfering with heartbeats. A
failure to connect to the server is triggering backoff, stopping progress from
being reported.
> There's little to be gained by putting a host into the penaltybox at reduce
> time, if its the only host you have
> ---------------------------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-935
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-935
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: tasktracker
> Affects Versions: 0.21.0
> Reporter: Steve Loughran
>
> Exponential backoff may be good for dealing with troublesome hosts, but not
> if you only have one host in the entire system. From the log of
> {{TestNodeRefresh}}, which for some reason is blocking in the reduce phase, I
> can see it doesn't take much for the backoff to kick in so rapidly that the
> reducer is waiting for longer than the test
> {code}
> 2009-08-28 21:39:16,788 WARN mapred.ReduceTask
> (ReduceTask.java:fetchOutputs(2192)) -
> attempt_20090828213826033_0001_r_000000_0 adding host localhost to penalty
> box, next contact in 150 seconds
> {code}
> The result of this backoff process is that the reduce process ends up
> appearing to hang, getting killed from above.
> Note that this isn't the root cause of the problem, but it certainly
> amplifies things.
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