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Date: Sat, 1 Apr 2006 16:37:27 +0100 (BST)
From: "eric baldeschwieler (JIRA)" <jira@apache.org>
To: hadoop-dev@lucene.apache.org
Subject: [jira] Commented: (HADOOP-115) 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.
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    [ http://issues.apache.org/jira/browse/HADOOP-115?page=comments#action_12372783 ] 

eric baldeschwieler commented on HADOOP-115:
--------------------------------------------

Ah!  Are you suggesting that getOutput* describes the final classes output from reduce always and if you don't set the new variables MapOutput* it also controls the map?  That is clear enough and backwards compatible.  I just was not looking at it the right way!


> 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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