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From Devaraj k <devara...@huawei.com>
Subject RE: Policies for placing a reducer
Date Tue, 16 Jul 2013 07:04:49 GMT

It doesn’t consider where the map’s ran to schedule the reducers because reducers need
to contact all the mappers for the map o/p’s.  It schedules reducers wherever the slots

Devaraj k

From: Felix.徐 [mailto:ygnhzeus@gmail.com]
Sent: 16 July 2013 09:25
To: user@hadoop.apache.org
Subject: Policies for placing a reducer

Hi all,

What is the policy of choosing a node for a reducer in mapreduce (Hadoop v1.2.0)?
For example,
If a cluster has 5 slaves, each slave can serve 2 maps and 2 reduces , there is a job who
occupies 5 mappers and 3 reducers , how does the jobtracker assign reducers to these nodes
(choosing free slaves or placing reducers close to mappers)?

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