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From Himanshu Vijay <himansh...@gmail.com>
Subject Cluster config: Mapper:Reducer Task Capapcity
Date Mon, 30 Sep 2013 19:39:41 GMT

Our Hadoop cluster is running 0.20.203. The cluster currently has 'Map Task
Capacity' of 8900+ 'Reduce Task Capacity' of 3300+ resulting in a ratio of
2.7. We have a lot of variety of jobs running and we want to increase the

My manual observation was that we hit the Mapper capacity and hence many
jobs have to wait even though lot of room left in Reduce capacity. I mined
the jobtracker logs for the jobs that completed and saw that on a hourly
basis as well as daily basis the mapper:reducer ratio was 4-5.

To increase the throughput I was thinking that I experiment changing the
Map and Reducer Task Capacity such that the ratio is increased from 2.7 to

Does this sound like a correct approach ? Is this something that I can
control or it's determined automatically by Hadoop ?

Have any of you done this kind of exercise ? If yes can you please direct
how to go about changing this ratio. I am not finding much literature on

Note: Mapper and ReducerTask Capacity is the max total no. of
mappers/reducers you can run on the cluster at any point.

-Himanshu Vijay

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