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https://issues.apache.org/jira/browse/HADOOP-4981?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12665727#action_12665727
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Arun C Murthy commented on HADOOP-4981:
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bq. In this case, returning nothing to the TT is a waste. You should move on to
the next job. So I need a way to tell me if the job potentially has a task to
run.
I have a slightly different take - I agree with the motivation, not with the
conclusion. We could just check if the highest priority job is _starved_ as
defined by our discussion in HADOOP-4667
(http://issues.apache.org/jira/browse/HADOOP-4667?focusedCommentId=12665726#action_12665726)
and use those apis to decide if we should move to the next job. Thoughts?
> 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
> Priority: Blocker
> Attachments: 4981.1.patch, 4981.2.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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