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Subject: RE: How can I control Number of Mappers of a job?
Date: Thu, 31 Jul 2008 10:47:53 +0530
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Thread-Topic: How can I control Number of Mappers of a job?
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From: "Goel, Ankur" <ankur.goel@corp.aol.com>
To: <core-user@hadoop.apache.org>
Cc: <core-dev@hadoop.apache.org>

How big is your cluster? Assuming you are running a single node cluster,

Hadoop-default.xml has a parameter 'mapred.map.tasks' that is set to 2.
So
By default, no matter how many map tasks are calculated by framework,
only  2 map task will execute on a single node cluster.

-----Original Message-----
From: Gopal Gandhi [mailto:gopal.gandhi2008@yahoo.com]=20
Sent: Thursday, July 31, 2008 4:38 AM
To: core-user@hadoop.apache.org
Cc: core-dev@hadoop.apache.org
Subject: How can I control Number of Mappers of a job?

The motivation is to control the max # of mappers of a job. For example,
the input data is 246MB, divided by 64M is 4. If by default there will
be 4 mappers launched on the 4 blocks.=20
What I want is to set its max # of mappers as 2, so that 2 mappers are
launched first and when they completes on the first 2 blocks, another 2
mappers start on the rest 2 blocks. Does Hadoop provide a way?


     =20