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https://issues.apache.org/jira/browse/MAPREDUCE-5124?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Peter Bacsko updated MAPREDUCE-5124:
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Attachment: MAPREDUCE-5124-CoalescingPOC-1.patch
I created a POC which uses this "event coalescing approach".
I roughly describe what changed:
* Added new method {{setNextUpdate()}} to {{TaskAttemptImpl}}
* Added the mapping of TaskAttemptID <-> TaskAttemptImpl
* At each {{statusUpdate()}}, we call {{setNextUpdate()}} and don't pass the
status object as a payload
* In the {{StatusUpdater}} transition, we check if we need to update the status
or not. If needsUpdate=true, then we run the original updater logic.
If we have backlog of task update events for a given attempt and that attempt
hasn't been updated, the {{StatusUpdater}} will not do anything because
{{needsUpdate}} will be false.
I also kept the original updating logic, that is, retrieving it from the event.
First I tried to remove the original constructor of
{{TaskAttemptStatusUpdateEvent}} but it caused compilation errors in various
classes. It turned out that quite a few test cases use the old approach to
manipulate the status of a task attempt. I didn't want to introduce too many
code changes. Not sure what's the best solution in this case.
[~jlowe] could you take a look at this POC?
> 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-CoalescingPOC-1.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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