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From Maria Stylianou <mars...@gmail.com>
Subject SimplePageRankComputation - The Reader behaves not as expected
Date Thu, 30 May 2013 10:53:33 GMT
Hey guys,

I was playing with PageRank these days, and had some weird results.
I wanted to use the Input Format Reader and Output Format Writer given
inside SimplePageRankComputation, so I gave my input file and called the
specific code in the command line.

Some of the vertices got value > 1. So I had a look in the logs, and
noticed that it is generating its own vertices and my input file is never
used.
The Vertex class inside the SimplePageRankVertexReader has the following
lines:
LongWritable vertexId = new LongWritable(
          (inputSplit.getSplitIndex() * totalRecords) + recordsRead);
      DoubleWritable vertexValue = new DoubleWritable(vertexId.get() * 10d);
      long targetVertexId =
          (vertexId.get() + 1) %
          (inputSplit.getNumSplits() * totalRecords);
      float edgeValue = vertexId.get() * 100f;

And in the Task Logs, it prints

2013-05-30 11:28:20,808 INFO
org.apache.giraph.examples.SimplePageRankVertex$SimplePageRankVertexReader:
next: Return vertexId=0, vertexValue=0.0, targetVertexId=1,
edgeValue=0.0
2013-05-30 11:28:20,809 INFO
org.apache.giraph.examples.SimplePageRankVertex$SimplePageRankVertexReader:
next: Return vertexId=1, vertexValue=10.0, targetVertexId=2,
edgeValue=100.0
2013-05-30 11:28:20,809 INFO
org.apache.giraph.examples.SimplePageRankVertex$SimplePageRankVertexReader:
next: Return vertexId=2, vertexValue=20.0, targetVertexId=3,
edgeValue=200.0
2013-05-30 11:28:20,809 INFO
org.apache.giraph.examples.SimplePageRankVertex$SimplePageRankVertexReader:
next: Return vertexId=3, vertexValue=30.0, targetVertexId=4,
edgeValue=300.0
2013-05-30 11:28:20,809 INFO
org.apache.giraph.examples.SimplePageRankVertex$SimplePageRankVertexReader:
next: Return vertexId=4, vertexValue=40.0, targetVertexId=5,
edgeValue=400.0
2013-05-30 11:28:20,809 INFO
org.apache.giraph.examples.SimplePageRankVertex$SimplePageRankVertexReader:
next: Return vertexId=5, vertexValue=50.0, targetVertexId=6,
edgeValue=500.0
2013-05-30 11:28:20,809 INFO
org.apache.giraph.examples.SimplePageRankVertex$SimplePageRankVertexReader:
next: Return vertexId=6, vertexValue=60.0, targetVertexId=7,
edgeValue=600.0
2013-05-30 11:28:20,810 INFO
org.apache.giraph.examples.SimplePageRankVertex$SimplePageRankVertexReader:
next: Return vertexId=7, vertexValue=70.0, targetVertexId=8,
edgeValue=700.0
2013-05-30 11:28:20,810 INFO
org.apache.giraph.examples.SimplePageRankVertex$SimplePageRankVertexReader:
next: Return vertexId=8, vertexValue=80.0, targetVertexId=9,
edgeValue=800.0
2013-05-30 11:28:20,810 INFO
org.apache.giraph.examples.SimplePageRankVertex$SimplePageRankVertexReader:
next: Return vertexId=9, vertexValue=90.0, targetVertexId=0,
edgeValue=900.0


Could someone explain why is this happening?
Thanks!
-- 
Maria Stylianou
Intern at Telefonica, Barcelona, Spain
Master Student of European Master in Distributed
Computing<http://www.kth.se/en/studies/programmes/master/em/emdc>
marsty5.wordpress.com

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