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https://issues.apache.org/jira/browse/MAPREDUCE-4507?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13427701#comment-13427701
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Bejoy KS commented on MAPREDUCE-4507:
-------------------------------------
Sorry About the typo
This piece of code will trigger ***{color:blue} IdentityMapper{color}
> IdentityMapper is being triggered when the type of the Input Key at class
> level and method level has a conflict
> ---------------------------------------------------------------------------------------------------------------
>
> Key: MAPREDUCE-4507
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4507
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: mrv1
> Affects Versions: 1.0.3
> Environment: linux ubuntu
> Reporter: Bejoy KS
>
> If we use the default InputFormat (TextInputFormat) but specify the Key type
> in mapper as IntWritable instead of Long Writable. The framework is supposed
> throw a class cast exception.Such an exception is thrown only if the key
> types at class level and method level are the same (IntWritable). But if we
> provide the Input key type as IntWritable on the class level but LongWritable
> on the method level (map method), instead of throwing a compile time error,
> the code compliles fine . In addition to it on execution the framework
> triggers Identity Mapper instead of the custom mapper provided with the
> configuration. In this case the 'mapreduce.map.class' in job.xml shows mapper
> as Custom Mapper itself , it should show IdentityMapper in cases where
> IdentityMapper is triggered to avoid confusion and easy debugging.
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