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https://issues.apache.org/jira/browse/MAPREDUCE-4089?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13244412#comment-13244412
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Vinod Kumar Vavilapalli commented on MAPREDUCE-4089:
----------------------------------------------------

In a sense, after this patch, we are again forcing users to set progress every 
so often either via a output write or an explict progress (perhaps in a 
separate thread). If users have to do it anyways, I don't see the purpose of 
the backgrounded (framework's) progress thread (that pings every three seconds).

But if it is just to be compatible, sure.

Either case, you should document the special meaning of zero timeout.
                
> Hung Tasks never time out. 
> ---------------------------
>
>                 Key: MAPREDUCE-4089
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4089
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mrv2
>    Affects Versions: 0.23.2, 2.0.0, trunk
>            Reporter: Robert Joseph Evans
>            Assignee: Robert Joseph Evans
>            Priority: Blocker
>         Attachments: MR-4089.txt, MR-4089.txt, MR-4089.txt
>
>
> The AM will timeout a task through mapreduce.task.timeout only when it does 
> not hear from the task within the given timeframe.  On 1.0 a task must be 
> making progress, either by reading input from HDFS, writing output to HDFS, 
> writing to a log, or calling a special method to inform it that it is still 
> making progress.
> This is because on 0.23 a status update which happens every 3 seconds is 
> counted as progress.

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