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https://issues.apache.org/jira/browse/MAPREDUCE-4897?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13537382#comment-13537382
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Harsh J commented on MAPREDUCE-4897:
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A simple workaround until this is resolved may be to add a job.setMapper(…)
call at the end of job configuration, after MI but before submit, causing it to
override MI's changes and making things work again.
> Using both MultipleInputs.addInputPath methods causes mappers to fail
> ---------------------------------------------------------------------
>
> Key: MAPREDUCE-4897
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-4897
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Affects Versions: 0.20.2
> Reporter: glad...@gmail.com
>
> The MultipleInputs class has two methods for adding inputs, one takes a
> mapper for the provided input path. When using both, both the inputformat
> gets set to DelegatingInputFormat class and the mapper class gets set to the
> DelegatingMapperClass.
> When running a map task, the delegating input sees theres no mapper for the
> provided input path, and the next step is to get the mapper from the jobconf
> (which usually defaults to the identity mapper). However, because I used both
> methods in the MultipleInputs class, the mapper in the jobconf is set to the
> DelegatingMapper. Thus the delegating mapper creates a delegating mapper and
> tries its map method. (this is how the framework gets the delegating mapper
> to use a provided mapper). And the map method sees no mapper created yet,
> creates a new delegating mapper, uses it, which see no mapper created yet,
> creates a delegating mapper, etc.
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