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https://issues.apache.org/jira/browse/MAPREDUCE-5221?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13677914#comment-13677914
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Tsuyoshi OZAWA commented on MAPREDUCE-5221:
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[~masokan]: I thought combinerClass can be removed from ReduceTask.java too.
However, combinerClass in ReduceTask.java is used to decide whether the
instance of CombineOutputCollector is created now. If it need to avoid being
instantiated, the combinerClass must remain. The instance seems to be not so
much expensive for me, so I think it can be removed. Do you have any opinion
about this?
> Reduce side Combiner is not used when using the new API
> -------------------------------------------------------
>
> Key: MAPREDUCE-5221
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5221
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Affects Versions: 2.0.4-alpha
> Reporter: Siddharth Seth
> Assignee: Tsuyoshi OZAWA
> Attachments: MAPREDUCE-5221.1.patch, MAPREDUCE-5221.2.patch,
> MAPREDUCE-5221.3.patch
>
>
> If a combiner is specified using o.a.h.mapreduce.Job.setCombinerClass - this
> will silently ignored on the reduce side since the reduce side usage is only
> aware of the old api combiner.
> This doesn't fail the job - since the new combiner key does not deprecate the
> old key.
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