pass mergeFunc to VertexPartitionBase, where merge is handled

Author: larryxiao

graphx/src/main/scala/org/apache/spark/graphx/VertexRDD.scala

@@ -410,10 +410,9 @@ object VertexRDD {
   def apply[VD: ClassTag](
       vertices: RDD[(VertexId, VD)], edges: EdgeRDD[_, _], defaultVal: VD, mergeFunc: (VD, VD) => VD
     ): VertexRDD[VD] = {
-    val verticesDedup = vertices.reduceByKey((VD1, VD2) => mergeFunc(VD1, VD2))
-    val vPartitioned: RDD[(VertexId, VD)] = verticesDedup.partitioner match {
-      case Some(p) => verticesDedup
-      case None => verticesDedup.copartitionWithVertices(new HashPartitioner(verticesDedup.partitions.size))
+    val vPartitioned: RDD[(VertexId, VD)] = vertices.partitioner match {
+      case Some(p) => vertices
+      case None => vertices.copartitionWithVertices(new HashPartitioner(vertices.partitions.size))
     }
     val routingTables = createRoutingTables(edges, vPartitioned.partitioner.get)
     val vertexPartitions = vPartitioned.zipPartitions(routingTables, preservesPartitioning = true) {

graphx/src/main/scala/org/apache/spark/graphx/impl/ShippableVertexPartition.scala

@@ -40,13 +40,14 @@ object ShippableVertexPartition {
 
   /**
    * Construct a `ShippableVertexPartition` from the given vertices with the specified routing
-   * table, filling in missing vertices mentioned in the routing table using `defaultVal`.
+   * table, filling in missing vertices mentioned in the routing table using `defaultVal`,
+   * and merging duplicate vertex atrribute with mergeFunc.
    */
   def apply[VD: ClassTag](
-      iter: Iterator[(VertexId, VD)], routingTable: RoutingTablePartition, defaultVal: VD)
+    iter: Iterator[(VertexId, VD)], routingTable: RoutingTablePartition, defaultVal: VD, mergeFunc: (VD, VD) => VD)
     : ShippableVertexPartition[VD] = {
     val fullIter = iter ++ routingTable.iterator.map(vid => (vid, defaultVal))
-    val (index, values, mask) = VertexPartitionBase.initFrom(fullIter, (a: VD, b: VD) => a)
+    val (index, values, mask) = VertexPartitionBase.initFrom(fullIter, mergeFunc)
     new ShippableVertexPartition(index, values, mask, routingTable)
   }