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From Kyle Orlando <>
Subject How to utilize combiners
Date Tue, 20 Aug 2013 18:51:57 GMT
Hey all,

I was wondering if there was any example code I could look at that uses a
combiner.  Creating your own Combiner is easy enough, e.g.
DoubleSumCombiner, but I am confused as to how/where I would use the
classes in my code.

For example, say I wanted to utilize the DoubleSumCombiner class to sum up
all of the messages arriving at a particular vertex at the beginning of the
superstep, and I wanted to do this for each vertex in the graph.  Where
should I instantiate a DoubleSumCombiner, when should I call the combine()
and createInitialMessage() methods, etc. in the compute() method?

What further confuses me is that I see that the MasterCompute class has
methods for setCombiner() and getCombiner(), and that there is also a
command line option -c to specify a Combiner.  I'm not really sure if these
are even necessary, but if they are, I don't know how these come into play

Some clarification or direction towards an example would be nice!

Kyle Orlando
Computer Engineering Major
University of Maryland

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