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Should we also allow specifying in the configure method? I suggest we deprecate the setting of output dataset from the configure method as it provides no utility over setting it in the beforeSubmit.
Naming of the MultipleOutputs class that we expose is up for change.
Should we allow the user to write to non-Dataset files from our MultipleOutputs class? I suggest no for simplicity. What this will disallow is the ability to write to both a Dataset and non-Dataset files from the same MapReduce.
Should we restrict users from simply calling context.write(k, v), after having set multiple Datasets as the output?