Jason Lowe commented on YARN-4088:

bq. See the problem with slower heartbeats is that if the tasks are 
short-running, there will be a cluster-wide throughput drop due to the feedback 
The nodemanager will do an out-of-band heartbeat if a container is killed, and 
IMHO should do the same when a container completes (not sure what's so special 
about killed vs. exiting wrt. scheduling).  Of course you can still get storms 
of heartbeats even though you explicitly tuned down the heartbeat interval if 
the cluster is churning containers at a very fast rate.

> RM should be able to process heartbeats from NM asynchronously
> --------------------------------------------------------------
>                 Key: YARN-4088
>                 URL: https://issues.apache.org/jira/browse/YARN-4088
>             Project: Hadoop YARN
>          Issue Type: Improvement
>          Components: resourcemanager, scheduler
>            Reporter: Srikanth Kandula
> Today, the RM sequentially processes one heartbeat after another. 
> Imagine a 3000 server cluster with each server heart-beating every 3s. This 
> gives the RM 1ms on average to process each NM heartbeat. That is tough.
> It is true that there are several underlying datastructures that will be 
> touched during heartbeat processing. So, it is non-trivial to parallelize the 
> NM heartbeat. Yet, it is quite doable...
> Parallelizing the NM heartbeat would substantially improve the scalability of 
> the RM, allowing it to either 
> a) run larger clusters or 
> b) support faster heartbeats or dynamic scaling of heartbeats
> c) take more asks from each application or 
> c) use cleverer/ more expensive algorithms such as node labels or better 
> packing or ...
> Indeed the RM's scalability limit has been cited as the motivating reason for 
> a variety of efforts which will become less needed if this can be solved. 
> Ditto for slow heartbeats.  See Sparrow and Mercury papers for example.
> Can we take a shot at this?
> If not, could we discuss why.

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