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https://issues.apache.org/jira/browse/MAPREDUCE-1126?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12802537#action_12802537
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Owen O'Malley commented on MAPREDUCE-1126:
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The problem is highlighted by this part of the patch:
{noformat}
- job.setMapOutputKeyClass(LongWritable.class);
- job.setMapOutputValueClass(BytesWritable.class);
+ WritableJobData.setMapOutputKeyClass(job.getConfiguration(),
+ LongWritable.class);
+ WritableJobData.setMapOutputValueClass(job.getConfiguration(),
+ BytesWritable.class);
{noformat}
That is a *really* ugly change to the user's application. If anything, I want
the api to infer the map output types from the Mapper's type parameters by
default.
We used to infer the serialization from the types. That was a clean model. Why
are you trying to change it? The type should imply a schema almost always. Am I
missing something? Why would someone want to set a schema separately from the
type?
Additionally, you have the framework depending on a library. That is a problem.
The right solution is to have a interface in mapreduce and have the library
code implement it.
> 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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