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https://issues.apache.org/jira/browse/YARN-8379?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16525285#comment-16525285
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Sunil Govindan commented on YARN-8379:
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Hi [~Zian Chen]
Few more comments
# In {{preemptOrkillSelectedContainerAfterWait}} could we avoid computing
toPreemptCount. Instead we can use toPreempt.size or something similar. Ideally
no: of containers in toPreempt and toPreemptPerSelector should be same.
#
{quote} we should give a clean curCandidates HashMap every time we call
editSchedule, otherwise like this UT, we call editschedule multiple times but
the selector remain the same instance
{quote}
To me, this is more likely a UT bug. As per the semantics, we do not need to
pass curCandidates and rather consider the return value alone.
# I think in line with above comments, we can try to rename
updateCurCandidates to updatePerSelectorCandidates and curCandidates to
something similar?
# May be more cleaner solution is to handle curCandidates map updates inside
CapacitySchedulerPreemptionUtils#addToPreemptMap method. All duplicate checks
are done before this method is called, so we can just add container to
curCandidates inside this method which avoid a lot of external handling and
cause more bugs later for new selector etc.
> Add an option to allow Capacity Scheduler preemption to balance satisfied
> queues
> --------------------------------------------------------------------------------
>
> Key: YARN-8379
> URL: https://issues.apache.org/jira/browse/YARN-8379
> Project: Hadoop YARN
> Issue Type: Bug
> Reporter: Wangda Tan
> Assignee: Zian Chen
> Priority: Major
> Attachments: YARN-8379.001.patch, YARN-8379.002.patch,
> YARN-8379.003.patch, YARN-8379.004.patch, YARN-8379.005.patch,
> ericpayne.confs.tgz
>
>
> Existing capacity scheduler only supports preemption for an underutilized
> queue to reach its guaranteed resource. In addition to that, there’s an
> requirement to get better balance between queues when all of them reach
> guaranteed resource but with different fairness resource.
> An example is, 3 queues with capacity, queue_a = 30%, queue_b = 30%, queue_c
> = 40%. At time T. queue_a is using 30%, queue_b is using 70%. Existing
> scheduler preemption won't happen. But this is unfair to queue_a since
> queue_a has the same guaranteed resources.
> Before YARN-5864, capacity scheduler do additional preemption to balance
> queues. We changed the logic since it could preempt too many containers
> between queues when all queues are satisfied.
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