[ http://issues.apache.org/jira/browse/HADOOP-115?page=all ]
Doug Cutting resolved HADOOP-115:
---------------------------------
Resolution: Won't Fix
This is the way it is supposed to work. From the MapReduce paper:
map (k1,v1) ! list(k2,v2)
reduce (k2,list(v2)) ! list(v2)
I.e., the input keys and values are drawn from a different
domain than the output keys and values. Furthermore,
the intermediate keys and values are from the same domain
as the output keys and values.
I am closing this bug. If someone feels strongly that we should extend the
MapReduce model in this direction, then we can re-open it. But, as it stands,
things work as intended.
> 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
>
> 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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