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From Sandy Ryza <sandy.r...@cloudera.com>
Subject Re: Cluster config: Mapper:Reducer Task Capapcity
Date Mon, 30 Sep 2013 19:52:23 GMT
Hi Himanshu,

Changing the ratio is definitely a reasonable thing to do.  The capacities
come from the mapred.tasktracker.map.tasks.maximum
and mapred.tasktracker.reduce.tasks.maximum tasktracker configurations.
 You can tweak these on your nodes to get your desired ratio.


On Mon, Sep 30, 2013 at 12:39 PM, Himanshu Vijay <himanshuvj@gmail.com>wrote:

> Hi,
> 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 throughput.
> 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
> ~4.
> 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
> it.
> Note: Mapper and ReducerTask Capacity is the max total no. of
> mappers/reducers you can run on the cluster at any point.
> Regards,
> -Himanshu Vijay

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