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https://issues.apache.org/jira/browse/MAPREDUCE-5124?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16261063#comment-16261063
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Jason Lowe commented on MAPREDUCE-5124:
---------------------------------------

I also kicked Jenkins which mysteriously did not comment on this patch.  It 
looks like there will be some checkstyle issues that should be addressed with 
exceeding 80 columns and other nitty things, but it'd also be good to see a 
unit test run.

> AM lacks flow control for task events
> -------------------------------------
>
>                 Key: MAPREDUCE-5124
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5124
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mr-am
>    Affects Versions: 2.0.3-alpha, 0.23.5
>            Reporter: Jason Lowe
>            Assignee: Peter Bacsko
>         Attachments: MAPREDUCE-5124-001.patch, 
> MAPREDUCE-5124-CoalescingPOC-1.patch, MAPREDUCE-5124-CoalescingPOC2.patch, 
> MAPREDUCE-5124-CoalescingPOC3.patch, MAPREDUCE-5124-proto.2.txt, 
> MAPREDUCE-5124-prototype.txt
>
>
> The AM does not have any flow control to limit the incoming rate of events 
> from tasks.  If the AM is unable to keep pace with the rate of incoming 
> events for a sufficient period of time then it will eventually exhaust the 
> heap and crash.  MAPREDUCE-5043 addressed a major bottleneck for event 
> processing, but the AM could still get behind if it's starved for CPU and/or 
> handling a very large job with tens of thousands of active tasks.



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