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From Eric Sammer <e...@lifeless.net>
Subject Re: Questions about JobTracker and TaskTracker
Date Mon, 11 Jan 2010 16:23:25 GMT
On 1/11/10 9:23 AM, psdc1978 wrote:
> Hi,
> 
> I've some questions about hadoop MapRed architecture:
> 
> 1 - It only exists one TaskTracker to one JobTracker?

Pedro:

There is a one JobTracker to many TaskTracker relationship. Generally,
all slave (worker machines) in a cluster run task trackers. The job
tracker is what clients will submit jobs to. I highly recommend the
Cloudera intro to HDFS and Mapred videos[2] or the Hadoop wiki[1] and
the getting started guide for the overview of the architecture.

> 2 - The Tasktracker and the JobTracker are two different instances that
> are started only through the start-mapred.sh script?

The start-mapred.sh script will start a job tracker on the node you run
the script on, if I'm not mistaken. It also ssh's to each node listed in
conf/slaves and starts a task tracker there as well.

> [snippet of start-mapred.sh]
> "$bin"/hadoop-daemon.sh --config $HADOOP_CONF_DIR start jobtracker
> "$bin"/hadoop-daemons.sh --config $HADOOP_CONF_DIR start tasktracker

[1] - http://wiki.apache.org/hadoop/
[2] - http://www.cloudera.com/hadoop-training-mapreduce-hdfs

Hope this helps.

-- 
Eric Sammer
eric@lifeless.net
http://esammer.blogspot.com

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