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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Closed: (HADOOP-115) permit reduce input types to differ from reduce output types
Date Mon, 05 Jun 2006 23:08:34 GMT
     [ http://issues.apache.org/jira/browse/HADOOP-115?page=all ]
Doug Cutting closed HADOOP-115:

> permit reduce input types to differ from reduce output types
> ------------------------------------------------------------
>          Key: HADOOP-115
>          URL: http://issues.apache.org/jira/browse/HADOOP-115
>      Project: Hadoop
>         Type: New Feature

>   Components: mapred
>     Reporter: Runping Qi
>     Assignee: Runping Qi
>      Fix For: 0.3.0
>  Attachments: hadoop-115_ReduceTask.patch, hadoop-115_tk.patch, patch_115.txt.2006_05_16
> 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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