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From Allen Wittenauer ...@apache.org>
Subject Re: controlling no. of mapper tasks
Date Wed, 22 Jun 2011 17:06:23 GMT

On Jun 20, 2011, at 12:24 PM, <praveen.peddi@nokia.com>
 <praveen.peddi@nokia.com> wrote:

> Hi there,
> I know client can send "mapred.reduce.tasks" to specify no. of reduce tasks and hadoop
honours it but "mapred.map.tasks" is not honoured by Hadoop. Is there any way to control number
of map tasks? What I noticed is that Hadoop is choosing too many mappers and there is an extra
overhead being added due to this. For example, when I have only 10 map tasks, my job finishes
faster than when Hadoop chooses 191 map tasks. I have 5 slave cluster and 10 tasks can run
in parallel. I want to set both map and reduce tasks to be 10 for max efficiency.


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