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From "Martin Kiefer (JIRA)" <j...@apache.org>
Subject [jira] [Created] (FLINK-1597) VertexCentricIterations create inefficient execution plans
Date Sun, 22 Feb 2015 16:12:11 GMT
Martin Kiefer created FLINK-1597:

             Summary: VertexCentricIterations create inefficient execution plans
                 Key: FLINK-1597
                 URL: https://issues.apache.org/jira/browse/FLINK-1597
             Project: Flink
          Issue Type: Bug
          Components: Gelly
    Affects Versions: master
            Reporter: Martin Kiefer

I did experiments with optimized versions of a graph algorithm that should utilize a secondary
sort on the edges and a trade off between superstep numbers and I/O. To my surprise the optimizations
did barely affect the execution times. I narrowed it down to inefficient execution plans.

I assumed that edge sets would be partitioned once at the beginning of a VertexCentricIteration
and never be touched again because they can not change during the iteration. I think this
should be the desired behavior. What actually happens is that UDFs creating the edge set are
pulled inside the iteration and are executed every superstep. This harms the performance of
graph algorithms significantly. 

As a simple example have a look at the execution plan generated for the PageRankExample:

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