1st paper for GraphX

"GraphX: A Resilient Distributed Graph System on Spark"
- GraphX: data-paralle + graph-parallel computation on graph
- data abstraction: Resilient Distributed Graph(RDG)
- graph splitting: Vertex-Cut
- testing dataset: LiveJournal(4.8 m vertices, 69 m edges)
- conclusion: 8X faster than Mahout/Hadoop, BUT 7X slower than
PowerGraph(GraphLab)
- hardware: Amazon EC2