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https://issues.apache.org/jira/browse/MAPREDUCE-3902?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13447943#comment-13447943
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Siddharth Seth commented on MAPREDUCE-3902:
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Thanks for the help with this JIRA.
bq. because MRAppMaster in container-reuse implementation has the feature to
monitor whether the running tasks on the containers are "the last task at a
machine or not", for the purpose of exiting JVMs on containers, as you know.
That will definitely be simpler to achieve with the container-reuse AM, with
nodes already tracking container information. Last task on a node can be
figured out relatively easily by the scheduler. It is, however, also possible
with the current AM, and several bits like the decision on when to run the
combiner - should be a straight forward port to the reuse-AM. IAC, it'll be
good to get the re-use AM into trunk fast. Looking forward to the updates on
4502 and 4525.
> 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: Siddharth Seth
> Attachments: MAPREDUCE-3902.2.patch, 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) : MAPREDUCE-4525
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