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https://issues.apache.org/jira/browse/HADOOP-3740?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12613537#action_12613537
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Vivek Ratan commented on HADOOP-3740:
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bq. I dont think allowing user code to run in JT is a good idea.

I wasn't referring to code written by a user (a person who uses Hadoop). I was 
talking of code written by a Hadoop developer. The Scheduling flow will provide 
hooks for developers to plug in their own code. 

> Make JobInProgress pluggable
> ----------------------------
>
>                 Key: HADOOP-3740
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3740
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: mapred
>         Environment: all
>            Reporter: Alejandro Abdelnur
>
> By allowing a pluggable JobInProgess it will be possible for provide 
> implementations that can do a sophisticated task provisioning to the 
> JobTracker. 
> For example, by providing alternate implementations of the 
> {{obtainNewMapTask}}, {{obtainNewReduceTask}} and {{updateTaskInProgress}} it 
> would be possible to implement a license server that allows to throttle use 
> of external resources (ie webservices, databases) so at any given time there 
> are not more than N tasks using a given resource. For this a task could be 
> tagged with the names of external resources and the license server would keep 
> track of the tasks running per tag, if the counter reaches zero then the 
> {{obtainNew*Task}} method could return NULL instead of a task.
>  

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