Sangjin Lee commented on YARN-3901:

Thanks for the updated patch [~vrushalic]! I went over the new patch, and the 
following is the quick feedback. I'll also apply it with YARN-4074, and test it 
a little more.

- l.141-155: the whole thing could be inside {{if (isApplication)...}}
- l.264: this null check is not needed

- l.52: Is the {{TimestampGenerator}} class going to be used outside 
{{FlowRunCoprocessor}}? If not, I would argue that we should make it an inner 
class of {{FlowRunCoprocessor}}. At least we should make it non-public to keep 
it within the package. If it would see general use outside this class, then it 
might be better to make it a true public class in the common package. I suspect 
a non-public class might be what we want here.
- l.52: let's make it final
- l.54: style nit: I think the common style is to place the static variables 
before instance variables
- Also, overall it seems we're using both the diamond operator (<>) and the old 
style generic declaration. It might be good to stick with one style (in which 
case the diamond operator might be better).
- l.144: This would mean that some cell timestamps would have the unit of the 
milliseconds and others would be in nanoseconds. I'm a little bit concerned if 
we ever interpret these timestamps incorrectly. Could there be a more explicit 
way of clearly differentiating them? I don't have good suggestions at the 

- variable ordering
- l.210: Strictly speaking, {{GenericObjectMapper}} will return an integer if 
the value fits within an integer; so it's not exactly a concern for min/max 
(timestamps) but for caution we might want to stay with {{Number}} instead of 

- l.29: make it final
- variable ordering
- see above for the public/non-public comment

- It's up to you, but you could leave the row key improvement to YARN-4074. 
That might be easier to manage the changes between yours and mine. I'm 
restructuring all *RowKey classes uniformly.

- it might be good to have short comments on what each method is testing

> Populate flow run data in the flow_run & flow activity tables
> -------------------------------------------------------------
>                 Key: YARN-3901
>                 URL: https://issues.apache.org/jira/browse/YARN-3901
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: timelineserver
>            Reporter: Vrushali C
>            Assignee: Vrushali C
>         Attachments: YARN-3901-YARN-2928.1.patch, 
> YARN-3901-YARN-2928.2.patch, YARN-3901-YARN-2928.3.patch, 
> YARN-3901-YARN-2928.4.patch
> As per the schema proposed in YARN-3815 in 
> https://issues.apache.org/jira/secure/attachment/12743391/hbase-schema-proposal-for-aggregation.pdf
> filing jira to track creation and population of data in the flow run table. 
> Some points that are being  considered:
> - Stores per flow run information aggregated across applications, flow version
> RM’s collector writes to on app creation and app completion
> - Per App collector writes to it for metric updates at a slower frequency 
> than the metric updates to application table
> primary key: cluster ! user ! flow ! flow run id
> - Only the latest version of flow-level aggregated metrics will be kept, even 
> if the entity and application level keep a timeseries.
> - The running_apps column will be incremented on app creation, and 
> decremented on app completion.
> - For min_start_time the RM writer will simply write a value with the tag for 
> the applicationId. A coprocessor will return the min value of all written 
> values. - 
> - Upon flush and compactions, the min value between all the cells of this 
> column will be written to the cell without any tag (empty tag) and all the 
> other cells will be discarded.
> - Ditto for the max_end_time, but then the max will be kept.
> - Tags are represented as #type:value. The type can be not set (0), or can 
> indicate running (1) or complete (2). In those cases (for metrics) only 
> complete app metrics are collapsed on compaction.
> - The m! values are aggregated (summed) upon read. Only when applications are 
> completed (indicated by tag type 2) can the values be collapsed.
> - The application ids that have completed and been aggregated into the flow 
> numbers are retained in a separate column for historical tracking: we don’t 
> want to re-aggregate for those upon replay

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