Apache Spark Graph Processing

The Pregel API in GraphX

Now, let's formalize the programming interface for the Pregel operator. Here is its definition:

class GraphOps[VD, ED] {
  def pregel[A]
      (initialMsg: A,
       maxIter: Int = Int.MaxValue,
       activeDir: EdgeDirection = EdgeDirection.Out)
      (vprog: (VertexId, VD, A) => VD,
       sendMsg: EdgeTriplet[VD, ED] => Iterator[(VertexId, A)],
       mergeMsg: (A, A) => A)
    : Graph[VD, ED]
}

The pregel method is invoked on a property graph, and returns a new graph with the same type and structure. While the edges remain intact, the attributes of the vertices may change from one superset to the next one. Pregel takes the following two lists of arguments. The first list contains:

• An initial message with a user-defined type A—this message is received by each vertex ...