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From "Owen O'Malley (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1216) Hadoop should support reduce none option
Date Tue, 10 Apr 2007 17:20:32 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1216?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12487830
] 

Owen O'Malley commented on HADOOP-1216:
---------------------------------------

I think this would be best represented as specifying  JobConf.setNumReduceTasks(0), which
would close HADOOP-357. In that case, sending the map output directly to the OutputFormat
would be appropriate. If the user doesn't want output from their map, they can just use NullOutputFormat
to swallow all outputs. It doesn't add any complexity to the config and fixes a current bug.
*smile*

> Hadoop should support reduce none option
> ----------------------------------------
>
>                 Key: HADOOP-1216
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1216
>             Project: Hadoop
>          Issue Type: New Feature
>          Components: mapred
>            Reporter: Runping Qi
>
> This has been a highly desired feature in streaming world and was asked occationally
in the non-streaming side.
> Streaming implemented a working (hacking) solution. But it also generates discrepency
between hadoop 
> streaming/non-streaming model. It would be nice if Hadoop offers such a feature 
> that works both streaming and non-streaming. Owen and I discussed this a bit and here
is the 
> general idea for further discussions/suggestions:
> 1. Allows the user to specify reducer=none in jobconf. 
> 2. The user still can specify output format and output directory
> 3. Each mapper will generate an output file in the specified directory. The naming convention
can still be like part-xxxxxxxx
> where xxxxxxxx is the map task number.
> 4. The mapoutput collector of a mapper task will be a record writer on the 
> 5. The mapper will call output.collect() to write the output, thus the same mapper class
can be 
> used, regardless reducer none is set or not.
> When reducer is set to none for a job, there will be no mapoutput files writen on to
local file system at all, 
> and no data shuffling between mappers and reducers. As a mapper of fact, the framework
may choose 
> not to create reducers at all.
>  

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