Hi,
Thanks a lot for the quick reply sir! We are new to Apache Hadoop and haven't
yet understood it properly yet. Can you please elaborate on how we can have
multiple stages of mapreduce jobs for combining the trails as you have
mentioned?
We have been trying to find out how to write a custom splitter and almost all
online resources tell to subclass the FileInputFormat and write only a custom
RecordReader? Will it be possible to generate our splits in that way?
Regards
Sharat
Date: Fri, 4 May 2012 09:22:51 -0700
Subject: Re: Ant Colony Optimization for Travelling Salesman Problem in Hadoop
From: lordjoe2...@gmail.com
To: mapreduce-user@hadoop.apache.org
On Fri, May 4, 2012 at 9:06 AM, sharat attupurath <shara...@hotmail.com> wrote:
Hi,
We are trying to parallelize the ant colony optimization
algorithm for TSP over hadoop and are facing some issues. We are using
TSPLIB as input files. The input is a text file containing eucledian
coordinates of the cities - first column is city number and the next two
columns contain the x and y coordinates respectively.
What we
intend to do is to take input from this single file, send copies of it
to multiple mappers (each mapper acts like the ant in the algorithm),
each mapper works on its input to find its own TSP solution that it
outputs and finally the reducer outputs the smallest tour found by the
mappers. Hope we are in the right track. Here are the issues:
1)
Since the input file is small, we need to force hadoop to fire up
multiple map tasks by replicating the input. How can we make an
InputSplit of the whole file and replicate it so that the input can be
sent to multiple mappers?
Write a custom splitter sending the same data to all mappers - the only
critical criteria is the number of "Ants"
2) the algorithm uses a shared
pheromone array and each mapper needs to read and write data from this.
How can we share the pheromone data across the mappers.
You cannot share data across mappers and should not attempt to do so - Better
to use the reducer(s) to combine trails combine first pass trails and
then pass the combined trails to another mapreduce job - this with the original
problem plus the current pheremone trails
Hope the questions are clear enough. Any help would be greatly appreciated.
Thank you
Regards
Sharat
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