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https://issues.apache.org/jira/browse/YARN-3434?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14488061#comment-14488061
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Thomas Graves commented on YARN-3434:
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{quote}
And I've a question about continous reservation checking behavior, may or may
not related to this issue: Now it will try to unreserve all containers under a
user, but actually it will only unreserve at most one container to allocate a
new container. Do you think is it fine to change the logic to be:
When (continousReservation-enabled) && (user.usage + required -
min(max-allocation, user.total-reserved) <=user.limit), assignContainers will
continue. This will prevent doing impossible allocation when user reserved lots
of containers. (As same as queue reservation checking).
{quote}
I do think the reservation checking and unreserving can be improved. I
basically started with very simple thing and figured we could improve. I'm not
sure how much that check would help in practice. I guess it might help the
cases where you have 1 user in the queue and a second one shows up and your
user limit gets decreased by a lot. In that case it may prevent it from
continuing when it can short circuit here. So it would seem to be ok for that.
> Interaction between reservations and userlimit can result in significant ULF
> violation
> --------------------------------------------------------------------------------------
>
> Key: YARN-3434
> URL: https://issues.apache.org/jira/browse/YARN-3434
> Project: Hadoop YARN
> Issue Type: Bug
> Components: capacityscheduler
> Affects Versions: 2.6.0
> Reporter: Thomas Graves
> Assignee: Thomas Graves
> Attachments: YARN-3434.patch
>
>
> ULF was set to 1.0
> User was able to consume 1.4X queue capacity.
> It looks like when this application launched, it reserved about 1000
> containers, each 8G each, within about 5 seconds. I think this allowed the
> logic in assignToUser() to allow the userlimit to be surpassed.
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