diff --git a/graph/src/main/scala/org/apache/spark/graph/Pregel.scala b/graph/src/main/scala/org/apache/spark/graph/Pregel.scala
index 1e59a39485..8e9ca89efc 100644
--- a/graph/src/main/scala/org/apache/spark/graph/Pregel.scala
+++ b/graph/src/main/scala/org/apache/spark/graph/Pregel.scala
@@ -105,7 +105,7 @@ object Pregel {
       // receive the messages
       val changedVerts = g.vertices.deltaJoin(messages)(vprog).cache() // updating the vertices
       // replicate the changed vertices
-      g = graph.deltaJoinVertices(changedVerts)
+      g = g.deltaJoinVertices(changedVerts)
       // count the iteration
       i += 1
     }
@@ -177,19 +177,19 @@ object Pregel {
     var g = graph.mapVertices( (vid, vdata) => vprog(vid, vdata, initialMsg) )
     // compute the messages
     var messages = g.mapReduceTriplets(sendMsgFun, mergeMsg).cache()
-    var activeMessages = messages.count
+    var activeMessages = messages.count()
     // Loop
     var i = 0
     while (activeMessages > 0) {
       // receive the messages
       val changedVerts = g.vertices.deltaJoin(messages)(vprog).cache() // updating the vertices
       // replicate the changed vertices
-      g = graph.deltaJoinVertices(changedVerts)
+      g = g.deltaJoinVertices(changedVerts)
 
       val oldMessages = messages
       // compute the messages
-      messages = g.mapReduceTriplets(sendMsgFun, mergeMsg).cache
-      activeMessages = messages.count
+      messages = g.mapReduceTriplets(sendMsgFun, mergeMsg).cache()
+      activeMessages = messages.count()
       // after counting we can unpersist the old messages
       oldMessages.unpersist(blocking=false)
       // count the iteration
diff --git a/graph/src/main/scala/org/apache/spark/graph/impl/VTableReplicated.scala b/graph/src/main/scala/org/apache/spark/graph/impl/VTableReplicated.scala
index 3e3769b9af..0c50ad09c7 100644
--- a/graph/src/main/scala/org/apache/spark/graph/impl/VTableReplicated.scala
+++ b/graph/src/main/scala/org/apache/spark/graph/impl/VTableReplicated.scala
@@ -2,7 +2,7 @@ package org.apache.spark.graph.impl
 
 import org.apache.spark.SparkContext._
 import org.apache.spark.rdd.RDD
-import org.apache.spark.util.collection.OpenHashSet
+import org.apache.spark.util.collection.{PrimitiveVector, OpenHashSet}
 
 import org.apache.spark.graph._
 
@@ -109,14 +109,23 @@ object VTableReplicated {
   def buildBuffer[VD: ClassManifest](pid2vidIter: Iterator[Array[Array[Vid]]], vertexPartIter: Iterator[VertexPartition[VD]]) = {
     val pid2vid: Array[Array[Vid]] = pid2vidIter.next()
     val vertexPart: VertexPartition[VD] = vertexPartIter.next()
-    val output = new Array[(Pid, VertexAttributeBlock[VD])](pid2vid.size)
-    //val output = mmm.newArray(pid2vid.size)
-    for (pid <- 0 until pid2vid.size) {
-      val block = new VertexAttributeBlock(
-        pid2vid(pid), pid2vid(pid).map(vid => vertexPart(vid)).toArray)
-      output(pid) = (pid, block)
+
+    Iterator.tabulate(pid2vid.size) { pid =>
+      val vidsCandidate = pid2vid(pid)
+      val size = vidsCandidate.length
+      val vids = new PrimitiveVector[Vid](pid2vid(pid).size)
+      val attrs = new PrimitiveVector[VD](pid2vid(pid).size)
+      var i = 0
+      while (i < size) {
+        val vid = vidsCandidate(i)
+        if (vertexPart.isDefined(vid)) {
+          vids += vid
+          attrs += vertexPart(vid)
+        }
+        i += 1
+      }
+      (pid, new VertexAttributeBlock(vids.trim().array, attrs.trim().array))
     }
-    output.iterator
   }
 }
 
diff --git a/graph/src/test/scala/org/apache/spark/graph/GraphSuite.scala b/graph/src/test/scala/org/apache/spark/graph/GraphSuite.scala
index fa4ebf3c88..514d20b76c 100644
--- a/graph/src/test/scala/org/apache/spark/graph/GraphSuite.scala
+++ b/graph/src/test/scala/org/apache/spark/graph/GraphSuite.scala
@@ -159,14 +159,20 @@ class GraphSuite extends FunSuite with LocalSparkContext {
       val star = Graph.fromEdgeTuples(sc.parallelize((1 to n).map(x => (0: Vid, x: Vid))), "v1").cache()
 
       // Modify only vertices whose vids are even
-      val newVerts = star.vertices.mapValues((vid, attr) => if (vid % 2 == 0) "v2" else attr)
-      val changedVerts = star.vertices.diff(newVerts)
+      val changedVerts = star.vertices.filter(_._1 % 2 == 0).mapValues((vid, attr) => "v2")
 
       // Apply the modification to the graph
-      val changedStar = star.deltaJoinVertices(newVerts, changedVerts)
+      val changedStar = star.deltaJoinVertices(changedVerts)
+
+      val newVertices = star.vertices.leftZipJoin(changedVerts) { (vid, oldVd, newVdOpt) =>
+        newVdOpt match {
+          case Some(newVd) => newVd
+          case None => oldVd
+        }
+      }
 
       // The graph's vertices should be correct
-      assert(changedStar.vertices.collect().toSet === newVerts.collect().toSet)
+      assert(changedStar.vertices.collect().toSet === newVertices.collect().toSet)
 
       // Send the leaf attributes to the center
       val sums = changedStar.mapReduceTriplets(