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https://issues.apache.org/jira/browse/MAPREDUCE-1287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12788792#action_12788792
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Tom White commented on MAPREDUCE-1287:
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What size of performance gain does this change give?
This might be better done in the framework, by using a special partitioner in
the single reduce case. A class called, say, SinglePartitionPartitioner whose
getPartition() method always returns 0.
> HashPartitioner calls hashCode() when there is only 1 reducer
> -------------------------------------------------------------
>
> Key: MAPREDUCE-1287
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1287
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Affects Versions: 0.22.0
> Reporter: Ed Mazur
> Priority: Minor
> Fix For: 0.22.0
>
> Attachments: MAPREDUCE-1287.2.patch, MAPREDUCE-1287.3.patch,
> MAPREDUCE-1287.patch
>
>
> HashPartitioner could be optimized to not call the key's hashCode() if there
> is only 1 reducer.
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