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https://issues.apache.org/jira/browse/MAPREDUCE-1126?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12805679#action_12805679
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Doug Cutting commented on MAPREDUCE-1126:
-----------------------------------------

Which Avro serializer? Avro includes three different mappings from in-memory to 
binary representations, and applications can add more. In generic, a 
java.lang.String represents an enum symbol, while in reflect it represents a 
string.

And do we really want to privilege Avro here? It should be possible to use 
Thrift too, and intermix the two within a single job. A Long in the input might 
be a part of Thrift union, and a Long in the output may use Avro.


> shuffle should use serialization to get comparator
> --------------------------------------------------
>
>                 Key: MAPREDUCE-1126
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-1126
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: task
>            Reporter: Doug Cutting
>            Assignee: Aaron Kimball
>             Fix For: 0.22.0
>
>         Attachments: MAPREDUCE-1126.2.patch, MAPREDUCE-1126.3.patch, 
> MAPREDUCE-1126.4.patch, MAPREDUCE-1126.5.patch, MAPREDUCE-1126.6.patch, 
> MAPREDUCE-1126.patch
>
>
> Currently the key comparator is defined as a Java class.  Instead we should 
> use the Serialization API to create key comparators.  This would permit, 
> e.g., Avro-based comparators to be used, permitting efficient sorting of 
> complex data types without having to write a RawComparator in Java.

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