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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-115) permit reduce input types to differ from reduce output types
Date Tue, 16 May 2006 23:26:10 GMT
     [ http://issues.apache.org/jira/browse/HADOOP-115?page=all ]

Doug Cutting updated HADOOP-115:
--------------------------------

        Summary: permit reduce input types to differ from reduce output types  (was: 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.)
           type: New Feature  (was: Improvement)
    Description: 
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.



  was:

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.




> 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
>  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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