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http://issues.apache.org/jira/browse/HADOOP-313?page=comments#action_12417531 ] 

Owen O'Malley commented on HADOOP-313:
--------------------------------------

Actually, it isn't for testing at all. It is for debugging a reduce crash in 
place on the production machines. Michel manually caught the reduce inputs, but 
in general we also need to add a configuration setting that lets a job request 
that some reduce task's inputs be kept. Maybe something like:
mapred.keep.reduce.inputs=...
Where the legal values are "all", "none", or a list of integers of which reduce 
tasks to keep the inputs for. 


> running a reduce task standalone
> --------------------------------
>
>          Key: HADOOP-313
>          URL: http://issues.apache.org/jira/browse/HADOOP-313
>      Project: Hadoop
>         Type: Bug

>     Reporter: Michel Tourn
>     Assignee: Michel Tourn
>  Attachments: sareduce.patch
>
> This is a tool to reproduce problems and to run unit tests involving a reduce 
> task.
> You just give it a reduce directory on the command line.
> Usage: java org.apache.hadoop.mapred.StandaloneReduceTask <taskdir> 
> [<limitmaps>]
> taskdir name encodes: task_<jobid>_r_<partition>_<attempt>
> taskdir contains job.xml and one or more input files named: map_<dddd>.out
> You should run with the same -Xmx option as the TaskTracker child JVM

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