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https://issues.apache.org/jira/browse/HADOOP-4749?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12653707#action_12653707
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Zheng Shao commented on HADOOP-4749:
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I think right after shuffling is done and before sorting is done (when the
reducer has got all mapper's output) we should already be able to know and
output those information.
> reducer should output input data size and record count when shuffling is done
> -----------------------------------------------------------------------------
>
> Key: HADOOP-4749
> URL: https://issues.apache.org/jira/browse/HADOOP-4749
> Project: Hadoop Core
> Issue Type: Improvement
> Components: mapred
> Reporter: Zheng Shao
>
> Sometimes we see a single slow reducer because of the load balancing problem.
> This information will be very useful to understand how imbalanced the load is.
> Should be easy to fix I guess, since reducer should have all information
> needed at the end of the shuffling phase.
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