Prior to Spark 1.2, there was no aggregateMessages method in Graph. Instead, the now deprecated mapReduceTriplets was the primary aggregation operator. The API for mapReduceTriplets is:

class Graph[VD, ED] {
  def mapReduceTriplets[Msg](
      map: EdgeTriplet[VD, ED] => Iterator[(VertexId, Msg)],
      reduce: (Msg, Msg) => Msg)
    : VertexRDD[Msg]
}

Compared to mapReduceTriplets, the new operator aggregateMessages is more expressive as it employs the message passing mechanism instead of returning an iterator of messages as mapReduceTriplets does. In addition, aggregateMessages explicitly requires the user to specify the TripletFields object for performance improvement as we explained previously. In addition to API improvements, aggregateMessages is optimized for performance.

Since mapReduceTriplets is now deprecated, we will not discuss it further. If you have to use it with earlier versions of Spark, you can refer to the Spark programming guide.