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https://issues.apache.org/jira/browse/MAPREDUCE-207?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12727170#action_12727170
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Matei Zaharia commented on MAPREDUCE-207:
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I think that's almost right, Philip. It looks to me like TASK_CLEANUP tasks can
be both maps and reduces. The JobTracker will launch them in a reduce slot if
they are cleaning up after a reducer. Therefore, isMapTask() might return false
when the task is a cleanup task. To check whether a given Task is a plain old
map task or plain old reduce task, you can use Task.isMapOrReduce().
This part of the code definitely leaves something to be desired. I believe Arun
mentioned he'd look at it as part of JobTracker refactoring in the future.
> Computing Input Splits on the MR Cluster
> ----------------------------------------
>
> Key: MAPREDUCE-207
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-207
> Project: Hadoop Map/Reduce
> Issue Type: New Feature
> Reporter: Philip Zeyliger
>
> Instead of computing the input splits as part of job submission, Hadoop could
> have a separate "job task type" that computes the input splits, therefore
> allowing that computation to happen on the cluster.
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