Siddharth Seth commented on TEZ-3405:


> Support ability for AM to kill itself if there is no client heartbeating to it
> ------------------------------------------------------------------------------
>                 Key: TEZ-3405
>                 URL: https://issues.apache.org/jira/browse/TEZ-3405
>             Project: Apache Tez
>          Issue Type: Bug
>            Reporter: Gunther Hagleitner
>            Assignee: Hitesh Shah
>            Priority: Critical
>         Attachments: TEZ-3405.1.patch, TEZ-3405.2.patch, TEZ-3405.3.patch, 
> TEZ-3405.4.patch, TEZ-3405.5.patch
> HiveServer2 optionally maintains a pool of AMs in either Tez or LLAP mode. 
> This is done to amortize the cost of launching a Tez session.
> We also try in a shutdown hook to kill all these AMs when HS2 goes down. 
> However, there are cases where HS2 doesn't get the chance to kill these AMs 
> before it goes away. As a result these zombie AMs hang around until the 
> timeout kicks in.
> The trouble with the timeout is that we have to set it fairly high. Otherwise 
> the benefit of having pre-launched AMs obviously goes away (in a lightly 
> loaded cluster).
> So, if people kill/restart HS2 they often times run into situations where the 
> cluster/queue doesn't have any more capacity for AMs. They either have to 
> manually kill the zombies or wait.
> The request is therefore for Tez to maintain a heartbeat to the client. If 
> the client goes away the AM should exit. That way we can keep the AMs alive 
> for a long time regardless of activity and at the same time don't have to 
> worry about them if HS2 goes down.

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