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https://issues.apache.org/jira/browse/YARN-1210?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13770457#comment-13770457
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Jian He commented on YARN-1210:
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Nowadays on NM resync with RM, all containers including AM is killed before NM
can reregister with RM. So the 1st AM should be guaranteed to exit before the
2nd AM is launched as long as they are running on the same machine. If the 2nd
AM is running on a different machine from the 1st AM, we may still see 2 AMs
running though.
> During RM restart, RM should start a new attempt only when previous attempt
> exits for real
> ------------------------------------------------------------------------------------------
>
> Key: YARN-1210
> URL: https://issues.apache.org/jira/browse/YARN-1210
> Project: Hadoop YARN
> Issue Type: Sub-task
> Reporter: Vinod Kumar Vavilapalli
> Assignee: Vinod Kumar Vavilapalli
>
> When RM recovers, it can wait for existing AMs to contact RM back and then
> kill them forcefully before even starting a new AM. Worst case, RM will start
> a new AppAttempt after waiting for 10 mins ( the expiry interval). This way
> we'll minimize multiple AMs racing with each other. This can help issues with
> downstream components like Pig, Hive and Oozie during RM restart.
> In the mean while, new apps will proceed as usual as existing apps wait for
> recovery.
> This can continue to be useful after work-preserving restart, so that AMs
> which can properly sync back up with RM can continue to run and those that
> don't are guaranteed to be killed before starting a new attempt.
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