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From "Konstantinos Karanasos (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-6593) [API] Introduce Placement Constraint object
Date Tue, 23 May 2017 18:51:04 GMT

    [ https://issues.apache.org/jira/browse/YARN-6593?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16021657#comment-16021657
] 

Konstantinos Karanasos commented on YARN-6593:
----------------------------------------------

bq. otherwise we have to check constraint-type everywhere
That's exactly the advantage of having a single simple constraint. When it is a target constraint,
min cardinality is 0 and max cardinality is infinite. When it is a cardinality constraint,
target is yourself. This way the scheduler has to deal with a single placement constraint.
No need for checking constraint-types at any point.

We keep it simple for the applications to express constraints through the utility methods,
and we keep it simple for the scheduler to deal with a single constraint type.

Moreover, if we have multiple classes for simple constraints, when building the objects from
the protobufs in the scheduler side, we will have to cast to each constraint class. And if
we decide to change those classes in the future (to expose a different way for users to write
constraints), we will have to change the way the scheduler deals with constraints, which should
really be avoided.

> [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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