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https://issues.apache.org/jira/browse/YARN-6710?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16056662#comment-16056662
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Yufei Gu commented on YARN-6710:
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Thanks [~daemon] for the detailed information.
Basically you are saying the latency of handling APP_ATTEMPT_REMOVED cause some
issues: 1) the amResourceUsage issue which has been fixed in YARN-3415, 2) RM
shouldn't assign any container to the application if its appAttempt has
finished and there are still resource requests. Issue 2 seems a legitimate
issue. For me, it is more a design issue in AM(Mapreduce, Spark) instead of RM
than an RM issue. I am not sure how the scheduler check the status of
application attempt for that situation. If the scheduler already know app
attempt has finished, it shouldn't assign any resources to it at all. Better to
check if that part is already here before we move on.
> There is a heavy bug in FSLeafQueue#amResourceUsage which will let the fair
> scheduler not assign container to the queue
> -----------------------------------------------------------------------------------------------------------------------
>
> Key: YARN-6710
> URL: https://issues.apache.org/jira/browse/YARN-6710
> Project: Hadoop YARN
> Issue Type: Bug
> Components: fairscheduler
> Affects Versions: 2.7.2
> Reporter: daemon
> Attachments: screenshot-1.png, screenshot-2.png, screenshot-3.png,
> screenshot-4.png, screenshot-5.png
>
>
> There are over three thousand nodes in my hadoop production cluster, and we
> use fair schedule as my scheduler.
> Though there are many free resource in my resource manager， but there are 46
> applications pending.
> Those applications can not run after several hours, and in the end I have to
> stop them.
> I reproduce the scene in my test environment, and I find a bug in
> FSLeafQueue.
> In a extreme scenario it will let the FSLeafQueue#amResourceUsage greater
> than itself.
> When fair scheduler try to assign container to a application attempt, it
> will do as follow check:
> !screenshot-2.png!
> !screenshot-3.png!
> Because the value of FSLeafQueue#amResourceUsage is invalid, it will greater
> then it real value.
> So when the value of amResourceUsage greater than the value of
> Resources.multiply(getFairShare(), maxAMShare) ,
> and the FSLeafQueue#canRunAppAM function will return false which will let the
> fair scheduler not assign container
> to the FSAppAttempt.
> In this scenario， all the application attempt will pending and never get any
> resource.
> I find the reason why so many applications in my leaf queue is pending. I
> will describe it as follow:
> When fair scheduler first assign a container to the application attempt, it
> will do something as blow:
> !screenshot-4.png!
> When fair scheduler remove the application attempt from the leaf queue, it
> will do something as blow:
> !screenshot-5.png!
> But when application attempt unregister itself, and all the container in the
> SchedulerApplicationAttempt#liveContainers
> are complete. There is a APP_ATTEMPT_REMOVED event will send to fair
> scheduler, but it is asynchronous.
> Before the application attempt is removed from FSLeafQueue, and there are
> pending request in FSAppAttempt.
> The fair scheduler will assign container to the FSAppAttempt, because the
> size of the liveContainers will equals to
> 1.
> So the FSLeafQueue will add to container resource to the
> FSLeafQueue#amResourceUsage, it will
> let the value of amResourceUsage greater then itself.
> In the end, the value of FSLeafQueue#amResourceUsage is preety large although
> there is no application
> it the queue.
> When new application come, and the value of FSLeafQueue#amResourceUsage
> greater than the value
> of Resources.multiply(getFairShare(), maxAMShare), it will let the scheduler
> never assign container to
> the queue.
> All of the applications in the queue will always pending.
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