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Date: Sun, 11 Jan 2009 05:50:50 -0800 (PST)
From: tienduc_dinh <tienduc_dinh@yahoo.com>
To: core-user@hadoop.apache.org
Subject: General questions about Map-Reduce
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hi,

I have some questions about Map-Reduce that I'm not sure, hope that you guys
can help me.

- Does Map-Reduce support parallel writing/reading ? 

I think not because I don't find anything like that in the source code. And
why the data of a input file are distributed on many data-nodes but the
parallel concept isn't used.

- What happens after the Map-Reduce operation ?

I got the first example on
http://hadoop.apache.org/core/docs/current/mapred_tutorial.html#Example%3A+WordCount+v1.0

So after the Map-Reduce operation we got

< Bye, 1>
< Goodbye, 1>
< Hadoop, 2>
< Hello, 2>
< World, 2> 

But how can I know that the input file will be written/read correctly on the
file system ?

Any help will be appreciated, thanks.

Tien Duc Dinh

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