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https://issues.apache.org/jira/browse/HADOOP-4981?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12710335#action_12710335
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Hemanth Yamijala commented on HADOOP-4981:
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+1 for the code changes. One minor point is to comment in the test case for the 
Fake objects that we are supporting only 1 speculative map / reduce at this 
point. I think this is enough for now. We can expand as needed.

> Prior code fix in Capacity Scheduler prevents speculative execution in jobs
> ---------------------------------------------------------------------------
>
>                 Key: HADOOP-4981
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4981
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: contrib/capacity-sched
>            Reporter: Vivek Ratan
>         Attachments: 4981.1.patch, 4981.2.patch, HADOOP-4981-1.patch, 
> HADOOP-4981-2.patch, HADOOP-4981-3.patch, HADOOP-4981-4.patch
>
>
> As part of the code fix for HADOOP-4035, the Capacity Scheduler obtains a 
> task from JobInProgress (calling obtainNewMapTask() or obtainNewReduceTask()) 
> only if the number of pending tasks for a job is greater than zero (see the 
> if-block in TaskSchedulingMgr.getTaskFromJob()). So, if a job has no pending 
> tasks and only has running tasks, it will never be given a slot, and will 
> never have a chance to run a speculative task. 

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