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Konstantinos Karanasos commented on YARN-7778:
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Thanks for the patch, [~cheersyang]. A couple of comments:
* Let's rename the getResourceConstraint() to something like
getMultilevelConstraint? Also the initial part of the comment "Retrieve the
placement constraint of a given scheduling request from the PCM point of view"
could be made more like "Consider all levels of constraints (resource request,
app, cluster) and return a merged constraint". This is because we can also
return a merged constraint of app and cluster level, even if there are no
resource request constraints.
* I would also change the signature of the method to add directly a Constraint
coming from the resource request and a set of tags, rather than pass the
SchedulingRequest object. This way we make clear that the set of tags is
separate from the specific constraint.
* Do we need the "Remove all null or duplicate constraints"? I was thinking
that this should belong to a separate step that will do constraint
simplification/minimization. If we keep it, I would suggest to put it in a
separate method in the PCM, so that we can use it elsewhere too or extend it in
the future easily.
> Merging of constraints defined at different levels
> --------------------------------------------------
>
> Key: YARN-7778
> URL: https://issues.apache.org/jira/browse/YARN-7778
> Project: Hadoop YARN
> Issue Type: Sub-task
> Reporter: Konstantinos Karanasos
> Assignee: Weiwei Yang
> Priority: Major
> Attachments: Merge Constraints Solution.pdf,
> YARN-7778-YARN-7812.001.patch, YARN-7778-YARN-7812.002.patch
>
>
> When we have multiple constraints defined for a given set of allocation tags
> at different levels (i.e., at the cluster, the application or the scheduling
> request level), we need to merge those constraints.
> Defining constraint levels as cluster > application > scheduling request,
> constraints defined at lower levels should only be more restrictive than
> those of higher levels. Otherwise the allocation should fail.
> For example, if there is an application level constraint that allows no more
> than 5 HBase containers per rack, a scheduling request can further restrict
> that to 3 containers per rack but not to 7 containers per rack.
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