[
https://issues.apache.org/jira/browse/HADOOP-6592?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12837117#action_12837117
]
Arun C Murthy commented on HADOOP-6592:
---------------------------------------
This keeps coming up occasionally...
Unfortunately people do not realize that this has significant (negative)
consequences to the cluster; in particular, map-outputs consume valuable
temporary storage and make this feature un-viable for Map-Reduce.
bq. If there's a bunch of "very low" priority tasks, they will still vie for
resources. Similarly, if I want to pause my task because I expect other tasks
to arrive (i.e., there are none queuing), very-low-pri doesn't quite fit the
bill.
Map-Reduce assumes that all dependencies are satisfied at time of
job-submission...
bq. 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).
You need pre-emption, not pause.
> 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.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
