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Date: Wed, 28 Nov 2012 17:38:59 +0000 (UTC)
From: "Robert Joseph Evans (JIRA)" <jira@apache.org>
To: mapreduce-issues@hadoop.apache.org
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Subject: [jira] [Commented] (MAPREDUCE-4819) AM can rerun job after
 reporting final job status to the client
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    [ https://issues.apache.org/jira/browse/MAPREDUCE-4819?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13505683#comment-13505683 ] 

Robert Joseph Evans commented on MAPREDUCE-4819:
------------------------------------------------

Yes, but going off of Koji's comments we also want to be sure that if the previous attempts edit log does not exist we don't know what state we were in and we should just assume we need to unregister and exit.
                
> AM can rerun job after reporting final job status to the client
> ---------------------------------------------------------------
>
>                 Key: MAPREDUCE-4819
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4819
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: mr-am
>    Affects Versions: 0.23.3, 2.0.1-alpha
>            Reporter: Jason Lowe
>            Assignee: Bikas Saha
>            Priority: Critical
>
> If the AM reports final job status to the client but then crashes before unregistering with the RM then the RM can run another AM attempt.  Currently AM re-attempts assume that the previous attempts did not reach a final job state, and that causes the job to rerun (from scratch, if the output format doesn't support recovery).
> Re-running the job when we've already told the client the final status of the job is bad for a number of reasons.  If the job failed, it's confusing at best since the client was already told the job failed but the subsequent attempt could succeed.  If the job succeeded there could be data loss, as a subsequent job launched by the client tries to consume the job's output as input just as the re-attempt starts removing output files in preparation for the output commit.

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