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https://issues.apache.org/jira/browse/MAPREDUCE-5583?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13794782#comment-13794782
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Arun C Murthy commented on MAPREDUCE-5583:
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[~jlowe] We can already accomplish this with queue/user limits? 

> Ability to limit running map and reduce tasks
> ---------------------------------------------
>
>                 Key: MAPREDUCE-5583
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5583
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: mr-am, mrv2
>    Affects Versions: 0.23.9, 2.1.1-beta
>            Reporter: Jason Lowe
>
> It would be nice if users could specify a limit to the number of map or 
> reduce tasks that are running simultaneously.  Occasionally users are 
> performing operations in tasks that can lead to DDoS scenarios if too many 
> tasks run simultaneously (e.g.: accessing a database, web service, etc.).  
> Having the ability to throttle the number of tasks simultaneously running 
> would provide users a way to mitigate issues with too many tasks on a large 
> cluster attempting to access a serivce at any one time.
> This is similar to the functionality requested by MAPREDUCE-224 and 
> implemented by HADOOP-3412 but was dropped in mrv2.



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