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Sangjin Lee commented on YARN-3367:
-----------------------------------

[~Naganarasimha] and I spoke offline about this, but wanted to recapture some 
of them.

I generally agree with the direction and the scope of the patch. The things 
that are being considered here are related enough that they should be handled 
as a whole.

Regarding clubbing asynchronous puts together in a single REST call, I wanted 
to be clear that its purpose is to reduce the overhead of the REST call 
latency. That said, we should be careful to keep buffering to a minimum as it 
would certainly complicate the picture in terms of handling put calls that 
arrive very late (that won't happen with the current patch).

Also, we should make sure the combined put REST call doesn't result in too big 
a payload. So in addition to combining calls, we should have a limitation on 
the size of the resulting PUT call. I don't think we need to be absolutely 
accurate here. We can use a simple measure (e.g. the number of entities + 
events + metrics, or even simply number of entities) to make sure things do not 
get out of control when put calls are made rapidly. I don't think this is an 
oft-occurring situation, but it would be good to have that safety.

Regarding the implementation of the async thread and the interaction with the 
workload:
ExecutorService is thread management plus work queue management, but at minimum 
we can use the thread management portion of things. That should help eliminate 
the need for the wait-notify done for shutting down the thread, coordinating 
with the thread shutdown, etc.

Also, instead of wait-nofity for the work completion, I would encourage using 
things like CountDownLatch or Future. Those will simplify code tremendously and 
also minimize room for errors. As a rule, I would advocate using higher level 
abstractions provided by java.util.concurrent over primitives, unless the 
concurrency utilities are not able to provide the right feature (which should 
be uncommon).

Another item: it would be good to have a self-contained "work item" instead of 
using a lookup on a map. For example, timeline entities + async flag can be a 
self-contained work item. Then it would be much simpler to deal with.

> Replace starting a separate thread for post entity with event loop in 
> TimelineClient
> ------------------------------------------------------------------------------------
>
>                 Key: YARN-3367
>                 URL: https://issues.apache.org/jira/browse/YARN-3367
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: timelineserver
>    Affects Versions: YARN-2928
>            Reporter: Junping Du
>            Assignee: Naganarasimha G R
>              Labels: yarn-2928-1st-milestone
>         Attachments: YARN-3367-feature-YARN-2928.003.patch, 
> YARN-3367-feature-YARN-2928.v1.002.patch, 
> YARN-3367-feature-YARN-2928.v1.004.patch, YARN-3367.YARN-2928.001.patch
>
>
> Since YARN-3039, we add loop in TimelineClient to wait for 
> collectorServiceAddress ready before posting any entity. In consumer of  
> TimelineClient (like AM), we are starting a new thread for each call to get 
> rid of potential deadlock in main thread. This way has at least 3 major 
> defects:
> 1. The consumer need some additional code to wrap a thread before calling 
> putEntities() in TimelineClient.
> 2. It cost many thread resources which is unnecessary.
> 3. The sequence of events could be out of order because each posting 
> operation thread get out of waiting loop randomly.
> We should have something like event loop in TimelineClient side, 
> putEntities() only put related entities into a queue of entities and a 
> separated thread handle to deliver entities in queue to collector via REST 
> call.



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