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http://issues.apache.org/jira/browse/HADOOP-115?page=comments#action_12373714 ]
Owen O'Malley commented on HADOOP-115:
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Your patch adds {set,get}MapOutputComparatorClass(), which aren't needed,
because the map outputs are the only ones that are compared.
I don't think you are handling the combiners.
Did you need to change the interfaces to explicitly pass around the key/value
types to the getRecordWriter()? Shouldn't getRecordWriter only be called for
the reduce outputs?
> Hadoop should allow the user to use SequentialFileOutputformat as the output
> format and to choose key/value classes that are different from those for map
> output.
> ------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: HADOOP-115
> URL: http://issues.apache.org/jira/browse/HADOOP-115
> Project: Hadoop
> Type: Improvement
> Components: mapred
> Reporter: Runping Qi
> Attachments: hadoop-115_tk.patch
>
> When map tasks write intermediate data out, they always use SequencialFile
> RecordWriter with key/value classes from the job object.
> When the reducers write the final results out, its output format is obtained
> from the job object. By default, it is TextOutputFormat, and no conflicts.
> However, if one wants to use SequencialFileFormat for the final results, then
> the key/value classes are also obtained from the job object, the same as the
> map tasks' output. Now we have a problem. It is impossible for the map
> outputs and reducer outputs use different key/value classes, if one wants the
> reducers generate outputs in SequentialFileFormat.
> A simple fix would be to add another two attributes to JobConf class:
> mapOutputLeyClass and mapOutputValueClass. That allows the user to have
> different key/value classes for the intermediate and final outputs.
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