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From "Bikas Saha (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-2001) Persist NMs info for RM restart
Date Tue, 06 May 2014 02:59:16 GMT

    [ https://issues.apache.org/jira/browse/YARN-2001?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13990220#comment-13990220

Bikas Saha commented on YARN-2001:

What if users want to have multiple standbys for fault tolerance? In a large 10000 nodes cluster
there could be 3-4 distinct fault domains where more than 1 standby may be good to guarantee
availability. Until now, in the design we have not restricted the number of standby's. Having
all NM's ping all RM's will cause a lot of communication overhead in a healthy cluster.
The design already encompasses NM's discovering and syncing with the new active RM. So that
is not the problem. The problem is restart during an upgrade where it may be common that a
bunch of NM's dont come back up. The RM needs to be resilient to that while maintaining availability.
Having a threshold of NM's sounds like a reasonable solution. The threshold can be calculated
based on the scheduling margin of error wrt queue capacity.

At this point my suggestion would be to clarify the problem being addressed in this jira.
Is the problem that after RM failover, the new RM needs to have a certain minimum number of
machines join it before it can safely make scheduling decisions? If thats the case then please
update the title to reflect that problem and not the solution.

> Persist NMs info for RM restart
> -------------------------------
>                 Key: YARN-2001
>                 URL: https://issues.apache.org/jira/browse/YARN-2001
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: resourcemanager
>            Reporter: Jian He
>            Assignee: Jian He
> RM should not accept allocate requests from AMs until all the NMs have registered with
RM. For that, RM needs to remember the previous NMs and wait for all the NMs to register.
> This is also useful for remembering decommissioned nodes across restarts.

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