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Hadoop >> mail # user >> Policies for placing a reducer

Felix.徐 2013-07-16, 03:55
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RE: Policies for placing a reducer

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 available.

Devaraj k

From: Felix.徐 [mailto:[EMAIL PROTECTED]]
Sent: 16 July 2013 09:25
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)?