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https://issues.apache.org/jira/browse/MAPREDUCE-1379?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12800621#action_12800621
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Bochun Bai commented on MAPREDUCE-1379:
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Matei, I use 1 with all the three parameters. The situation of starving tasks 
do exists, numTotal > numMap && numTotal > numReduce will improve it.
A custom scheduler solve the situation too, but in different layer and a little 
bit more difficult. I will try to implement one later.


> Limit both numMapTasks and numReduceTasks
> -----------------------------------------
>
>                 Key: MAPREDUCE-1379
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1379
>             Project: Hadoop Map/Reduce
>          Issue Type: New Feature
>          Components: tasktracker
>    Affects Versions: 0.22.0
>            Reporter: Bochun Bai
>            Priority: Trivial
>         Attachments: limit-both-numMapTasks-and-numReduceTasks.patch
>
>
> In some environment, the number of concurrent running process is very 
> sensitive.
>   mapreduce.tasktracker.map.tasks.maximum
> and
>   mapreduce.tasktracker.reduce.tasks.maximum
> limit tasks running on each tasktracker separately.
> This patch limits them together, using 
> mapreduce.tasktracker.total.tasks.maximum

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