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https://issues.apache.org/jira/browse/YARN-2113?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15941308#comment-15941308
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Wangda Tan commented on YARN-2113:
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[~sunilg], thanks for update the patch.
Checked the patch and also offline discussed with Sunil, I can understand that
this patch handles an edge case which allows a lower priority app preempt
higher priority app if the user of higher priority app beyond its user limit.
However I think it is debatable: as of now, YARN doesn't calculate UL for
different priorities, but that doesn't mean we should allow lower priority app
to preempt higher priority app. [~eepayne], could you share your thoughts here?
And also, this patch added a compound comparator which sort application in
following way (essentially): {{(priority > demand) > (fifo > demand)}}
I'm a little worried about this complex comparator. If we could decide no lower
priority app can preempt higher priority app. We should be able to simply
compare logic to:
{code}
compare(a, b)
if (a.priority != b.priority) {
return a.priority.compare(b.priority)
}
return a.toBePreemptFromOther.compare(b.toBePreemptFromOther)
{code}
Above logic makes sure that when priority is same, app with
toBePreemptFromOther always goes first. Is it possible that one app's
toBePreemptFromOther > 0 and actuallyToBePreempted > 0 at the same time? If it
is possible, could you add some examples?
> Add cross-user preemption within CapacityScheduler's leaf-queue
> ---------------------------------------------------------------
>
> Key: YARN-2113
> URL: https://issues.apache.org/jira/browse/YARN-2113
> Project: Hadoop YARN
> Issue Type: Sub-task
> Components: scheduler
> Reporter: Vinod Kumar Vavilapalli
> Assignee: Sunil G
> Attachments: YARN-2113.0001.patch, YARN-2113.0002.patch,
> YARN-2113.0003.patch, YARN-2113.v0.patch
>
>
> Preemption today only works across queues and moves around resources across
> queues per demand and usage. We should also have user-level preemption within
> a queue, to balance capacity across users in a predictable manner.
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