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https://issues.apache.org/jira/browse/YARN-1769?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Thomas Graves updated YARN-1769:
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Attachment: YARN-1769.patch
update if check in assignContainer
> CapacityScheduler: Improve reservations
> ----------------------------------------
>
> Key: YARN-1769
> URL: https://issues.apache.org/jira/browse/YARN-1769
> Project: Hadoop YARN
> Issue Type: Improvement
> Components: capacityscheduler
> Affects Versions: 2.3.0
> Reporter: Thomas Graves
> Assignee: Thomas Graves
> Attachments: YARN-1769.patch, YARN-1769.patch
>
>
> Currently the CapacityScheduler uses reservations in order to handle requests
> for large containers and the fact there might not currently be enough space
> available on a single host.
> The current algorithm for reservations is to reserve as many containers as
> currently required and then it will start to reserve more above that after a
> certain number of re-reservations (currently biased against larger
> containers). Anytime it hits the limit of number reserved it stops looking
> at any other nodes. This results in potentially missing nodes that have
> enough space to fullfill the request.
> The other place for improvement is currently reservations count against your
> queue capacity. If you have reservations you could hit the various limits
> which would then stop you from looking further at that node.
> The above 2 cases can cause an application requesting a larger container to
> take a long time to gets it resources.
> We could improve upon both of those by simply continuing to look at incoming
> nodes to see if we could potentially swap out a reservation for an actual
> allocation.
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