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https://issues.apache.org/jira/browse/MAPREDUCE-1126?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12805283#action_12805283
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Doug Cutting commented on MAPREDUCE-1126:
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> Should we still consider separating the concerns of key/value class type and
> key/value serialization method?
Jay, with union types there is no single class save Object that all keys and
values in a job must share. So the key/value classes for some jobs are not
very useful or interesting. Consider, e.g., Pig's data model, where things are
either a bag. tuple or a built-in type (int, long, String, float double, etc.).
For tests, a job that uses Avro would be better off validating the data
against the schema than checking whether a particular class is used.
> 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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