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https://issues.apache.org/jira/browse/HADOOP-6592?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12837109#action_12837109
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Adam Kramer commented on HADOOP-6592:
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Similarly, if paused during the map phase, any reducers already allocated
(which couldn't, in theory, begin working until all mappers complete) would be
killed and freed. (so yes, the copy would need to restart, but the reducers
wouldn't be held hostage by huge map tasks).
> Scheduler: Pause button desirable
> ---------------------------------
>
> Key: HADOOP-6592
> URL: https://issues.apache.org/jira/browse/HADOOP-6592
> Project: Hadoop Common
> Issue Type: Wish
> Reporter: Adam Kramer
> Priority: Minor
>
> It would be lovely if, from the jobtracker page, I could click a button
> that's not "kill" or "fail" but ..."pause."
> The pause button would stop a certain task from starting any more mappers or
> reducers. They would all wait in the "pending" stage until the job is
> "un-paused." Currently-running tasks would continue to run, and then
> complete, thus freeing the resources for other jobs.
> This would help a lot for systems (esp. Hive) in which one or two jobs are
> hogging a lot of mappers or reducers. The ones they have would finish, and
> then other jobs could "catch up," and then they could be unpaused for a
> while. This would also allow for user-level throttling of their jobs in
> instances where they need a lot of resources but have the time to spare.
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