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https://issues.apache.org/jira/browse/MAPREDUCE-6513?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14965222#comment-14965222
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chong chen commented on MAPREDUCE-6513:
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Another way to think about this. Current reducer ramp up and down are designed
to handle normal case, like this one "slowstart.completedmaps config here was
0.05". Once all mapper tasks are scheduled and allocated, AM already submits
all reducers to the system. At this stage, it is a nature thinking to handle
failure mapper as abnormal case rather than resetting the whole thing and going
through ramp up/down again.
> MR job got hanged forever when one NM unstable for some time
> ------------------------------------------------------------
>
> Key: MAPREDUCE-6513
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-6513
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: applicationmaster, resourcemanager
> Affects Versions: 2.7.0
> Reporter: Bob
> Assignee: Varun Saxena
> Priority: Critical
>
> when job is in-progress which is having more tasks,one node became unstable
> due to some OS issue.After the node became unstable, the map on this node
> status changed to KILLED state.
> Currently maps which were running on unstable node are rescheduled, and all
> are in scheduled state and wait for RM assign container.Seen ask requests for
> map till Node is good (all those failed), there are no ask request after
> this. But AM keeps on preempting the reducers (it's recycling).
> Finally reducers are waiting for complete mappers and mappers did n't get
> container..
> My Question Is:
> ============
> why map requests did not sent AM ,once after node recovery.?
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