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From: Harsh J <harsh@cloudera.com>
Date: Sun, 12 Aug 2012 19:48:42 +0530
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 <CAOcnVr140m8Fx6TbHgr_LSg9aC+z7DkfiQJsPf=HiX2LfHt2mQ@mail.gmail.com>
Subject: Re: Hadoop cluster/monitoring
To: common-dev@hadoop.apache.org
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Nagaraju,

On Wed, Aug 8, 2012 at 10:52 PM, Nagaraju Bingi
<nagaraju_bingi@persistent.co.in> wrote:
> Hi,
>
> I'm beginner in Hadoop concepts. I have few basic questions:
> 1) looking for APIs to retrieve the capacity of the cluster. so that i can write a script to when to add a new slave node to the cluster
>
>              a) No.of Task trackers and  capacity of  each task tracker  to spawn  max No.of Mappers

For this, see: http://hadoop.apache.org/common/docs/stable/api/org/apache/hadoop/mapred/ClusterStatus.html

>               b) CPU,RAM and disk capacity of each tracker

Rely on other tools to provide this one. Tools such as Ganglia and
Nagios can report this, for instance.

>               c) how to decide to add a new  slave node to the cluster

This is highly dependent on the workload that is required out of your clusters.

>  2) what is the API to retrieve metrics like current usage of resources and currently running/spawned Mappers/Reducers

See 1.a. for some, and 1.b for some more.

>  3) what is the purpose of Hadoop-common?Is it API to interact with hadoop

Hadoop Common encapsulates the utilities shared by both of the other
sub-projects - MapReduce and HDFS. Among other things, it does provide
a general interaction API for all things 'Hadoop'

-- 
Harsh J