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https://issues.apache.org/jira/browse/YARN-7774?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16331868#comment-16331868
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Weiwei Yang commented on YARN-7774:
-----------------------------------
Hi [~asuresh]
In \{{DefaultPlacementAlgorithm}}, for each SchedulingRequest, it iterates over
available nodes and each time it attempts to allocate one allocation on a node,
then go to next node. Imagine the request asks for 2 allocations affinity on
same node, does it mean the second allocation can only be made after it
iterates all nodes again? This algorithm doesn't seem to be affinity friendly.
{\{CircularIterator}} looks to be general enough and deserves its own class
with a generic type, it can be moved to common package. Also it would be good
to add some test case for it. It doesn't have to be done in this patch. Just a
suggestion.
Hope this helps. Thanks
> Miscellaneous fixes to the PlacementProcessor
> ---------------------------------------------
>
> Key: YARN-7774
> URL: https://issues.apache.org/jira/browse/YARN-7774
> Project: Hadoop YARN
> Issue Type: Sub-task
> Reporter: Arun Suresh
> Assignee: Arun Suresh
> Priority: Blocker
> Attachments: YARN-7774-YARN-6592.001.patch,
> YARN-7774-YARN-6592.002.patch, YARN-7774-YARN-6592.003.patch,
> YARN-7774-YARN-6592.004.patch
>
>
> JIRA to track the following minor changes:
> * Scheduler must normalize requests that are made using the
> {{attemptAllocationOnNode}} method.
> * Currently, the placement algorithm resets the node iterator for each
> request. The Placement Algorithm should either shuffle the node iterator OR
> use a circular iterator - to ensure a) more nodes are looked at and b) bias
> against placing too many containers on the same node
> * Add a placement retry loop for rejected requests - since there are cases
> especially, when Constraints will be satisfied after a subsequent request has
> been placed.
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