Varun Saxena commented on YARN-4224:

Well, we can have a generic REST query without entity type as well. I was just 
saying that it would require scanning quite a bit of entity table.
We would not want users to use it. If we make it public, users may use it and 
that query maybe slow. If that is acceptable, then we can go ahead wit it.
I doubt we will be able to support querying generic entities(i.e. querying all 
entities irrespective of entity type for an app) in a faster manner, especially 
if users write a lot of generic entities, even in future. 
Thoughts [~sjlee0] ?

bq. we can even say return one random entity within the given application
Yes, but that has to be scoped within entity type. Entity ID + Entity type 
uniquely identify an entity, merely entity ID doesnt.

bq. "on this end point I assume you want all entities for this application, but 
to avoid crash myself I'm only returning a part of it" looks fine
Again, as I mentioned the problem here is how do we stop. We guarantee entities 
will be ordered by created time. So we will have to scan all possible records 
for that row prefix to return rows upto a limit(100 or 200 or whatever). If 
scanning so many records is acceptable, we can have it, supporting it as such 
wont be a big issue. We should ideally restrict scanning as less records as 
possible(for default use case) because it can be a performance hog.

> Change the ATSv2 reader side REST interface to conform to current REST APIs' 
> in YARN
> ------------------------------------------------------------------------------------
>                 Key: YARN-4224
>                 URL: https://issues.apache.org/jira/browse/YARN-4224
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: timelineserver
>    Affects Versions: YARN-2928
>            Reporter: Varun Saxena
>            Assignee: Varun Saxena
>              Labels: yarn-2928-1st-milestone
>         Attachments: YARN-4224-YARN-2928.01.patch, 
> YARN-4224-feature-YARN-2928.wip.02.patch

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