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https://issues.apache.org/jira/browse/YARN-6593?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16021533#comment-16021533
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Konstantinos Karanasos commented on YARN-6593:
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Thanks, [~leftnoteasy].
What I realized is that we are trying to define at the same time the internal
representation that will be used by the scheduler and the one that will be
user-friendly.
I think we should split the two. I suggest to keep the java classes
implementing the PBImpls to be in sync with them, and then add a utility class
that allows users to create constraints in a more intuitive way. The utility
class can expose all the constraint creation methods and hide all the protobuf
details (e.g., the fact that we have a PlacementConstraint class internally).
This will allow us to evolve separately the way users specify constraints
without needing to change the PBImpl classes or their subclasses etc.
Moreover, we can create a string utility method that can parse a string
representation of the constraints and create PBImpl objects, which I think will
be really useful too.
Let me know what you guys think.
BTW, the reason I have not created separate classes for target and cardinality
constraints is that I we also have the more general constraint (the one we
mention as "cluster operator constraint" in the document, such as "don't allow
more than 5 ZooKeeper containers per rack") that includes all three. So I don't
see the use of adding three different classes for this. Especially if we have
the utility class I mentioned above.
PS: I forgot to reply to [~pg1...@imperial.ac.uk], since we chatted offline,
but I am adding it here for completeness. Unfortunately protobuf 2.5, which is
still the required version in Hadoop, does not support the {{extends}}
construct to define sub/superclasses in the protobufs.
> [API] Introduce Placement Constraint object
> -------------------------------------------
>
> Key: YARN-6593
> URL: https://issues.apache.org/jira/browse/YARN-6593
> Project: Hadoop YARN
> Issue Type: Sub-task
> Reporter: Konstantinos Karanasos
> Assignee: Konstantinos Karanasos
> Attachments: YARN-6593.001.patch, YARN-6593.002.patch
>
>
> This JIRA introduces an object for defining placement constraints.
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