[jira] [Updated] (MAPREDUCE-3902) MR AM should reuse containers for map tasks, there-by allowing fine-grained control on num-maps for users without need for CombineFileInputFormat etc.

["Arun C Murthy (Updated) (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MAPREDUCE-3902?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Arun C Murthy updated MAPREDUCE-3902:
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    Summary: MR AM should reuse containers for map tasks, there-by allowing fine-grained control on num-maps for users without need for CombineFileInputFormat etc.  (was: MR AM should reuse containers for map tasks)

bq. Is there a cap on the amount of re-use?  For example, if the container has been in use for more than 1 minute then do not re-use it.

Not currently, but we could add something like this - except it won't make too much difference since you need to run the remaining maps in other containers anyway! :)

bq. Or to rephrase, what prevents a cluster with a few large jobs from having hogged containers?

The central scheduler (e.g CapacityScheduler) already uses queue-capacities and user-limits, (and in future, preemption) to prevent this.
                
> MR AM should reuse containers for map tasks, there-by allowing fine-grained control on num-maps for users without need for CombineFileInputFormat etc.
> ------------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: MAPREDUCE-3902
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-3902
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: applicationmaster, mrv2
>            Reporter: Arun C Murthy
>            Assignee: Arun C Murthy
>         Attachments: MAPREDUCE-3902.patch
>
>
> The MR AM is now in a great position to reuse containers across (map) tasks. This is something similar to JVM re-use we had in 0.20.x, but in a significantly better manner:
> # Consider data-locality when re-using containers
> # Consider the new shuffle - ensure that reduces fetch output of the whole container at once (i.e. all maps) 

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