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From "Jason Lowe (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-3730) Allow restarted NM to rejoin cluster before RM expires it
Date Thu, 16 Feb 2012 04:40:59 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-3730?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13209113#comment-13209113
] 

Jason Lowe commented on MAPREDUCE-3730:
---------------------------------------

Thanks Vinod for taking another look.  The race condition mentioned above isn't specific to
the new node approach, as it's still present when modifying the original RMNode.  A node could
rejoin just as the tracker service expires it, and we could mark the node as lost (new or
original node object, doesn't matter) just as it starts to heartbeat in again.

I still think using a new node object is easier to implement, understand, and maintain since
it more directly mirrors the existing behavior of a node that eventually expires and starts
again.  However I'll defer to your judgement and update the patch accordingly.

Note that using ephemeral ports can be problematic, as it opens the door to inadvertent duplicate
NM registration and the problems described in MAPREDUCE-3363.  I believe all of our clusters
are currently configured to not use them.  We should reconsider the ephemeral port default
once this goes in, since it was only changed to workaround the NM rejoin issue.
                
> Allow restarted NM to rejoin cluster before RM expires it
> ---------------------------------------------------------
>
>                 Key: MAPREDUCE-3730
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-3730
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: mrv2, resourcemanager
>    Affects Versions: 0.23.1, 0.24.0
>            Reporter: Jason Lowe
>            Assignee: Jason Lowe
>            Priority: Minor
>             Fix For: 0.23.2
>
>         Attachments: MAPREDUCE-3730.patch, MAPREDUCE-3730.patch
>
>
> When a node in the RUNNING state (healthy or unhealthy) is rebooted, the resourcemanager
rejects the nodemanager's registration request as a duplicate because it is convinced that
the nodemanager is already running on that node.  It won't allow that node to rejoin the cluster
until the node expiration time elapses which is 10min+ by default.  We should allow the NM
to rejoin the cluster if it re-registers within the expiration timeout.
> Note that this problem occurs with NMs that are configured to specific ports.  If ephemeral
ports are used then a NM reboot "works" because the RM thinks the NM registration is for a
new node.  See the discussions in MAPREDUCE-3070 and MAPREDUCE-3363.

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