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https://issues.apache.org/jira/browse/YARN-5715?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15593274#comment-15593274
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Sangjin Lee commented on YARN-5715:
-----------------------------------

The jenkins appears to be unstable right now, and that might be why the build 
hasn't kicked in.

I think the latest patch is almost there. Should this be committed to trunk? We 
know that more parts to the reader code are needed. Should we wait until those 
parts are done before we commit this to trunk? Is this needed on the trunk now?

(TimelineEntity.java)
- l.597: nit: “Set” -> “Sets”
- also, for “user”, let’s say either “users” or “the user”
- Can we move the statement “User can use …” to the end of the javadoc (after 
“Entities will be stored…”)? IMO it is more important to state that the 
entities will be stored in the id prefix order than how to invert the prefix.

(TimelineServiceHelper.java)
- l.50: nit: “Invert” -> “Inverts”

(EntityRowKey.java)
- l.230: we should use “long” here (not “Long”)


> introduce entity prefix for return and sort order
> -------------------------------------------------
>
>                 Key: YARN-5715
>                 URL: https://issues.apache.org/jira/browse/YARN-5715
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: timelineserver
>            Reporter: Sangjin Lee
>            Assignee: Rohith Sharma K S
>            Priority: Critical
>         Attachments: YARN-5715-YARN-5355.01.patch, 
> YARN-5715-YARN-5355.02.patch, YARN-5715-YARN-5355.03.patch, 
> YARN-5715-YARN-5355.04.patch, YARN-5715-YARN-5355.05.patch
>
>
> While looking into YARN-5585, we have come across the need to provide a sort 
> order different than the current entity id order. The current entity id order 
> returns entities strictly in the lexicographical order, and as such it 
> returns the earliest entities first. This may not be the most natural return 
> order. A more natural return/sort order would be from the most recent 
> entities.
> To solve this, we would like to add what we call the "entity prefix" in the 
> row key for the entity table. It is a number (long) that can be easily 
> provided by the client on write. In the row key, it would be added before the 
> entity id itself.
> The entity prefix would be considered mandatory. On all writes (including 
> updates) the correct entity prefix should be set by the client so that the 
> correct row key is used. The entity prefix needs to be unique only within the 
> scope of the application and the entity type.
> For queries that return a list of entities, the prefix values will be 
> returned along with the entity id's. Queries that specify the prefix and the 
> id should be returned quickly using the row key. If the query omits the 
> prefix but specifies the id (query by id), the query may be less efficient.
> This JIRA should add the entity prefix to the entity API and add its handling 
> to the schema and the write path. The read path will be addressed in 
> YARN-5585.



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