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https://issues.apache.org/jira/browse/HADOOP-4620?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12653676#action_12653676
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Sharad Agarwal commented on HADOOP-4620:
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Had a discussion on this Devaraj. It seems there aren't reasonable usecase
which may require outputting from reducer with no input. It should be ok to not
output anything from reducer with no input. However hang problem should be
fixed for it as well.
> Streaming mapper never completes if the mapper does not write to stdout
> -----------------------------------------------------------------------
>
> Key: HADOOP-4620
> URL: https://issues.apache.org/jira/browse/HADOOP-4620
> Project: Hadoop Core
> Issue Type: Bug
> Components: mapred
> Affects Versions: 0.17.2
> Reporter: Runping Qi
> Assignee: Ravi Gummadi
> Attachments: solves_mapper_4620.patch
>
>
> A mapper of a streaming job has empty input data and thus it produces no
> output.
> The task never completes.
> The following are the last two lines from the task log:
> 2008-11-07 21:59:48,254 INFO org.apache.hadoop.streaming.PipeMapRed:
> PipeMapRed exec [/usr/bin/perl, xxx]
> 2008-11-07 21:59:48,330 INFO org.apache.hadoop.streaming.PipeMapRed:
> mapRedFinished
>
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