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https://issues.apache.org/jira/browse/MAPREDUCE-4961?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13562505#comment-13562505
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Jerry Chen commented on MAPREDUCE-4961:
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The point here is that since the shuffle is pluggable we don't know how the
shuffle copy the data as well as how the shuffle merge the data.
The only thing is call it's run method and use the returned
RawKeyValueIterator, although for local running, the copy phase can be skipped,
we may still need respect the Shuffle plugin have the right to merge the data
other ways.
> Map reduce running local should also go through ShuffleConsumerPlugin for
> enabling different MergeManager implementations
> -------------------------------------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-4961
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4961
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Affects Versions: trunk
> Reporter: Jerry Chen
> Assignee: Tsuyoshi OZAWA
> Original Estimate: 72h
> Remaining Estimate: 72h
>
> MAPREDUCE-4049 provide the ability for pluggable Shuffle and MAPREDUCE-4080
> extends Shuffle to be able to provide different MergeManager implementations.
> While using these pluggable features, I find that when a map reduce is
> running locally, a RawKeyValueIterator was returned directly from a static
> call of Merge.merge, which break the assumption that the Shuffle may provide
> different merge methods although there is no copy phase for this situation.
> The use case is when I am implementating a hash-based MergeManager, we don't
> need sort in map side, while when running the map reduce locally, the
> hash-based MergeManager will have no chance to be used as it goes directly to
> Merger.merge. This makes the pluggable Shuffle and MergeManager incomplete.
> So we need to move the code calling Merger.merge from Reduce Task to
> ShuffleConsumerPlugin implementation, so that the Suffle implementation can
> decide how to do the merge and return corresponding iterator.
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