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https://issues.apache.org/jira/browse/MAPREDUCE-114?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12844234#action_12844234
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Qi Liu commented on MAPREDUCE-114:
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Yes, it is related.
> All reducer tasks are finished, while some mapper tasks are still running
> -------------------------------------------------------------------------
>
> Key: MAPREDUCE-114
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-114
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Reporter: Qi Liu
> Attachments: hadoop-bug-overview.png, hadoop-bug-useless-task.png
>
>
> In a high load environment (i.e. multiple jobs are queued up to be executed),
> when all reducer tasks of a job are finished, some mapper tasks of the same
> job may still running (possibly re-executed due to lost task tracker, etc).
> This should not happen when a job has at least one reducer task. When all
> reducer tasks are in SUCCEEDED state, the Hadoop JobTracker should kill all
> running mapper tasks, since execution would be meaningless. The job should
> also switch to SUCCEEDED state when all reducer tasks of that job succeeded
> successfully.
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