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https://issues.apache.org/jira/browse/MAPREDUCE-4328?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13395841#comment-13395841
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Kang Xiao commented on MAPREDUCE-4328:
--------------------------------------

It is useful in some condition such as NN is down. Actually we find a way to 
achieve the first goal by updating the fair scheduler's conf set each pool's 
max share to be zero. 
The second goal will protect the job from going to FAILED. But it seems so 
possible for a job to go to FAILED since no more task scheduled.

It may be more simple to just not invoke assignTasks() in JobTracker to 
implement the first goal. And it will not burden the scheduler implementation 
since 'safemode' is a small probability event.
                
> Add the option to quiesce the JobTracker
> ----------------------------------------
>
>                 Key: MAPREDUCE-4328
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4328
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: mrv1
>    Affects Versions: 1.0.3
>            Reporter: Arun C Murthy
>            Assignee: Arun C Murthy
>         Attachments: MAPREDUCE-4328.patch
>
>
> In several failure scenarios it would be very handy to have an option to 
> quiesce the JobTracker.
> Recently, we saw a case where the NameNode had to be rebooted at a customer 
> due to a random hardware failure - in such a case it would have been nice to 
> not lose jobs by quiescing the JobTracker.

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