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https://issues.apache.org/jira/browse/MAPREDUCE-4808?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13537070#comment-13537070
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Tom White commented on MAPREDUCE-4808:
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These changes look reasonable to me. The changes in MapOutput means Fetcher
doesn't know if the shuffle is in-memory or on-disk - it's hidden behind the
MapOutput shuffle() method - which is an improved separation of concerns.
MergeManagerPlugin is then free to return whatever implementations of MapOutput
that it likes.
* It wasn't immediately obvious to me that returning null in
MergeManager#reserve() means "wait" (since the "wait" type of MapOutput has
gone). It would be good to have a comment to that effect.
* It would be good to have javadoc for the methods on MergeManagerPlugin.
* In TestMergeManagerPlugin the try/catch blocks can be avoided by making the
tests throw the relevant exception.
> Allow reduce-side merge to be pluggable
> ---------------------------------------
>
> Key: MAPREDUCE-4808
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4808
> Project: Hadoop Map/Reduce
> Issue Type: New Feature
> Affects Versions: 2.0.2-alpha
> Reporter: Arun C Murthy
> Assignee: Mariappan Asokan
> Fix For: 2.0.3-alpha
>
> Attachments: COMBO-mapreduce-4809-4812-4808.patch,
> mapreduce-4808.patch, mapreduce-4808.patch, mapreduce-4808.patch
>
>
> Allow reduce-side merge to be pluggable for MAPREDUCE-2454
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