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.
From: Felix.徐 [mailto:[EMAIL PROTECTED]]
Sent: 16 July 2013 09:25
To: [EMAIL PROTECTED]
Subject: Policies for placing a reducer
What is the policy of choosing a node for a reducer in mapreduce (Hadoop v1.2.0)?
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)?