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https://issues.apache.org/jira/browse/HADOOP-4143?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12629895#action_12629895
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Doug Cutting commented on HADOOP-4143:
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> Unfortunately, Partitioner is an interface [ ... ] 

This is a non-issue with HADOOP-1230.  If this feature is needed soon, then we 
should push harder on that one.

That said, I'm still not clear on the motivation.  Is it performance?  
Comparators already provide both raw and cooked comparisons.  If a partitioner 
is defined in terms of a comparator, it must currently used a cooked 
comparison, which might be slower.  If this is a performance issue, then we 
should measure the potential performance improvement with a benchmark before we 
consider the API change.  Are there non-performance reasons for this change?

> Support for a "raw" Partitioner that partitions based on the serialized key 
> and not record objects
> --------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-4143
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4143
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: mapred
>            Reporter: Chris Douglas
>         Attachments: 4143-0.patch
>
>
> For some partitioners (particularly those using comparators to classify 
> keys), it would be helpful if one could specify a "raw" partitioner that 
> would receive the serialized version of the key rather than the object 
> emitted from the map.

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