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https://issues.apache.org/jira/browse/MAPREDUCE-2454?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13503401#comment-13503401
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Mariappan Asokan commented on MAPREDUCE-2454:
---------------------------------------------

Hi Laxman,
  The way the Shuffle plugin is defined, it can complement the Merger plugin or 
it can act alone in order to generate the final merged output.

In the former case, the shuffle plugin can implement accelerated shuffling in 
software or in hardware+software combination.  You can still use a Merger 
plugin to do the merge.

In the latter case(this is what is referred as "Network Levitated Merge" in the 
paper you mention), the Shuffle plugin itself can do the shuffle+merge.  In 
this case, the Shuffle plugin can choose to ignore the Merger plugin.

In essence, with individual units pluggable you get more choices and not 
restrictions.

-- Asokan
                
> Allow external sorter plugin for MR
> -----------------------------------
>
>                 Key: MAPREDUCE-2454
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2454
>             Project: Hadoop Map/Reduce
>          Issue Type: New Feature
>    Affects Versions: 2.0.0-alpha, 3.0.0, 2.0.2-alpha
>            Reporter: Mariappan Asokan
>            Assignee: Mariappan Asokan
>            Priority: Minor
>              Labels: features, performance, plugin, sort
>         Attachments: HadoopSortPlugin.pdf, HadoopSortPlugin.pdf, 
> KeyValueIterator.java, MapOutputSorterAbstract.java, MapOutputSorter.java, 
> mapreduce-2454-modified-code.patch, mapreduce-2454-modified-test.patch, 
> mapreduce-2454-new-test.patch, mapreduce-2454.patch, mapreduce-2454.patch, 
> mapreduce-2454.patch, mapreduce-2454.patch, mapreduce-2454.patch, 
> mapreduce-2454.patch, mapreduce-2454.patch, mapreduce-2454.patch, 
> mapreduce-2454.patch, mapreduce-2454.patch, mapreduce-2454.patch, 
> mapreduce-2454.patch, mapreduce-2454.patch, mapreduce-2454.patch, 
> mapreduce-2454.patch, mapreduce-2454.patch, mapreduce-2454.patch, 
> mapreduce-2454.patch, mapreduce-2454.patch, mapreduce-2454.patch, 
> mapreduce-2454.patch, mapreduce-2454-protection-change.patch, 
> mr-2454-on-mr-279-build82.patch.gz, MR-2454-trunkPatchPreview.gz, 
> ReduceInputSorter.java
>
>
> Define interfaces and some abstract classes in the Hadoop framework to 
> facilitate external sorter plugins both on the Map and Reduce sides.

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