diff --git a/graph/src/main/scala/org/apache/spark/graph/Graph.scala b/graph/src/main/scala/org/apache/spark/graph/Graph.scala
index 86502182fb..a0907c319a 100644
--- a/graph/src/main/scala/org/apache/spark/graph/Graph.scala
+++ b/graph/src/main/scala/org/apache/spark/graph/Graph.scala
@@ -278,7 +278,7 @@ abstract class Graph[VD: ClassManifest, ED: ClassManifest] {
       (mapFunc: (Vid, VD, Option[U]) => VD2)
     : Graph[VD2, ED]
 
-  def deltaJoinVertices(newVerts: VertexRDD[VD], changedVerts: VertexRDD[VD]): Graph[VD, ED]
+  def deltaJoinVertices(changedVerts: VertexRDD[VD]): Graph[VD, ED]
 
   // Save a copy of the GraphOps object so there is always one unique GraphOps object
   // for a given Graph object, and thus the lazy vals in GraphOps would work as intended.
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 ffbb6fe3ca..1e59a39485 100644
--- a/graph/src/main/scala/org/apache/spark/graph/Pregel.scala
+++ b/graph/src/main/scala/org/apache/spark/graph/Pregel.scala
@@ -103,12 +103,9 @@ object Pregel {
       // compute the messages
       val messages = g.mapReduceTriplets(sendMsg, mergeMsg) // broadcast & aggregation
       // receive the messages
-      val newVerts = g.vertices.zipJoin(messages)(vprog).cache() // updating the vertices
-      val changedVerts = g.vertices.diff(newVerts)
-      println("Replicating %d changed vertices instead of %d total vertices".format(
-        changedVerts.count, newVerts.count))
+      val changedVerts = g.vertices.deltaJoin(messages)(vprog).cache() // updating the vertices
       // replicate the changed vertices
-      g = graph.deltaJoinVertices(newVerts, changedVerts)
+      g = graph.deltaJoinVertices(changedVerts)
       // count the iteration
       i += 1
     }
@@ -185,12 +182,9 @@ object Pregel {
     var i = 0
     while (activeMessages > 0) {
       // receive the messages
-      val newVerts = g.vertices.zipJoin(messages)(vprog).cache() // updating the vertices
-      val changedVerts = g.vertices.diff(newVerts)
-      println("Replicating %d changed vertices instead of %d total vertices".format(
-        changedVerts.count, newVerts.count))
+      val changedVerts = g.vertices.deltaJoin(messages)(vprog).cache() // updating the vertices
       // replicate the changed vertices
-      g = graph.deltaJoinVertices(newVerts, changedVerts)
+      g = graph.deltaJoinVertices(changedVerts)
 
       val oldMessages = messages
       // compute the messages
diff --git a/graph/src/main/scala/org/apache/spark/graph/VertexRDD.scala b/graph/src/main/scala/org/apache/spark/graph/VertexRDD.scala
index 5afe2df0ca..1b8ab89ebe 100644
--- a/graph/src/main/scala/org/apache/spark/graph/VertexRDD.scala
+++ b/graph/src/main/scala/org/apache/spark/graph/VertexRDD.scala
@@ -207,6 +207,14 @@ class VertexRDD[@specialized VD: ClassManifest](
     }
   }
 
+  def deltaJoin[VD2: ClassManifest]
+      (other: VertexRDD[VD2])(f: (Vid, VD, VD2) => VD): VertexRDD[VD] =
+  {
+    this.zipVertexPartitions(other) { (thisPart, otherPart) =>
+      thisPart.deltaJoin(otherPart)(f)
+    }
+  }
+
   /**
    * Left join this VertexSet with another VertexSet which has the
    * same Index.  This function will fail if both VertexSets do not
diff --git a/graph/src/main/scala/org/apache/spark/graph/impl/GraphImpl.scala b/graph/src/main/scala/org/apache/spark/graph/impl/GraphImpl.scala
index 6e9566e060..4300812990 100644
--- a/graph/src/main/scala/org/apache/spark/graph/impl/GraphImpl.scala
+++ b/graph/src/main/scala/org/apache/spark/graph/impl/GraphImpl.scala
@@ -239,9 +239,13 @@ class GraphImpl[VD: ClassManifest, ED: ClassManifest] protected (
     new GraphImpl(newVTable, edges, vertexPlacement)
   }
 
-  override def deltaJoinVertices(
-      newVerts: VertexRDD[VD],
-      changedVerts: VertexRDD[VD]): Graph[VD, ED] = {
+  override def deltaJoinVertices(changedVerts: VertexRDD[VD]): Graph[VD, ED] = {
+    val newVerts = vertices.leftZipJoin(changedVerts) { (vid, oldAttr, newAttrOpt) =>
+      newAttrOpt match {
+        case Some(newAttr) => newAttr
+        case None => oldAttr
+      }
+    }
     val newVTableReplicated = new VTableReplicated(
       changedVerts, edges, vertexPlacement, Some(vTableReplicated))
     new GraphImpl(newVerts, edges, vertexPlacement, newVTableReplicated)
diff --git a/graph/src/main/scala/org/apache/spark/graph/impl/VertexPartition.scala b/graph/src/main/scala/org/apache/spark/graph/impl/VertexPartition.scala
index c922350345..0af445fa7d 100644
--- a/graph/src/main/scala/org/apache/spark/graph/impl/VertexPartition.scala
+++ b/graph/src/main/scala/org/apache/spark/graph/impl/VertexPartition.scala
@@ -127,6 +127,30 @@ class VertexPartition[@specialized(Long, Int, Double) VD: ClassManifest](
     }
   }
 
+  /** Inner join another VertexPartition. */
+  def deltaJoin[VD2: ClassManifest, VD3: ClassManifest]
+      (other: VertexPartition[VD2])
+      (f: (Vid, VD, VD2) => VD3): VertexPartition[VD3] =
+  {
+    if (index != other.index) {
+      logWarning("Joining two VertexPartitions with different indexes is slow.")
+      join(createUsingIndex(other.iterator))(f)
+    } else {
+      val newValues = new Array[VD3](capacity)
+      val newMask = mask & other.mask
+
+      var i = newMask.nextSetBit(0)
+      while (i >= 0) {
+        newValues(i) = f(index.getValue(i), values(i), other.values(i))
+        if (newValues(i) == values(i)) {
+          newMask.unset(i)
+        }
+        i = mask.nextSetBit(i + 1)
+      }
+      new VertexPartition(index, newValues, newMask)
+    }
+  }
+
   /** Left outer join another VertexPartition. */
   def leftJoin[VD2: ClassManifest, VD3: ClassManifest]
       (other: VertexPartition[VD2])