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From Owen O'Malley <omal...@apache.org>
Subject Re: Only running hadoop Map tasks
Date Tue, 05 Jan 2010 18:32:04 GMT

On Jan 5, 2010, at 9:13 AM, psdc1978 wrote:

> 1 - I would like to see what is output that the Maps is doing on my
> example. Is it possible to put hadoop only running Map tasks,
> excluding the Reduce tasks?

Set the number of reduce tasks to 0.

> 2 - The output of the Maps is written into a temporary file?

Each map's unsorted output will be sent to the OutputFormat, which  
writes it to the output directory.

> 3 - How the output of the maps is passed to the reduce tasks? Is using
> a socket or reading a file in the disk?

MapReduce does not assume any shared disks between machines. The map  
outputs are transfered via http.

-- Owen


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