[SPARK-5461] [graphx] Add isCheckpointed, getCheckpointedFiles methods to Graph

Added the 2 methods to Graph and GraphImpl.  Both make calls to the underlying vertex and edge RDDs.

This is needed for another PR (for LDA): [https://github.com/apache/spark/pull/4047]

Notes:
* getCheckpointedFiles is plural and returns a Seq[String] instead of an Option[String].
* I attempted to test to make sure the methods returned the correct values after checkpointing.  It did not work; I guess that checkpointing does not occur quickly enough?  I noticed that there are not checkpointing tests for RDDs; is it just hard to test well?

CC: rxin

CC: mengxr  (since related to LDA)

Author: Joseph K. Bradley <joseph@databricks.com>

Closes #4253 from jkbradley/graphx-checkpoint and squashes the following commits:

b680148 [Joseph K. Bradley] added class tag to firstParent call in VertexRDDImpl.isCheckpointed, though not needed to compile
250810e [Joseph K. Bradley] In EdgeRDDImple, VertexRDDImpl, added transient back to partitionsRDD, and made isCheckpointed check firstParent instead of partitionsRDD
695b7a3 [Joseph K. Bradley] changed partitionsRDD in EdgeRDDImpl, VertexRDDImpl to be non-transient
cc00767 [Joseph K. Bradley] added overrides for isCheckpointed, getCheckpointFile in EdgeRDDImpl, VertexRDDImpl. The corresponding Graph methods now work.
188665f [Joseph K. Bradley] improved documentation
235738c [Joseph K. Bradley] Added isCheckpointed and getCheckpointFiles to Graph, GraphImpl

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

@@ -104,6 +104,18 @@ abstract class Graph[VD: ClassTag, ED: ClassTag] protected () extends Serializab
    */
   def checkpoint(): Unit
 
+  /**
+   * Return whether this Graph has been checkpointed or not.
+   * This returns true iff both the vertices RDD and edges RDD have been checkpointed.
+   */
+  def isCheckpointed: Boolean
+
+  /**
+   * Gets the name of the files to which this Graph was checkpointed.
+   * (The vertices RDD and edges RDD are checkpointed separately.)
+   */
+  def getCheckpointFiles: Seq[String]
+
   /**
    * Uncaches both vertices and edges of this graph. This is useful in iterative algorithms that
    * build a new graph in each iteration.

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

@@ -73,7 +73,15 @@ class EdgeRDDImpl[ED: ClassTag, VD: ClassTag] private[graphx] (
   override def checkpoint() = {
     partitionsRDD.checkpoint()
   }
-    
+
+  override def isCheckpointed: Boolean = {
+    firstParent[(PartitionID, EdgePartition[ED, VD])].isCheckpointed
+  }
+
+  override def getCheckpointFile: Option[String] = {
+    partitionsRDD.getCheckpointFile
+  }
+
   /** The number of edges in the RDD. */
   override def count(): Long = {
     partitionsRDD.map(_._2.size.toLong).reduce(_ + _)

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

@@ -70,6 +70,17 @@ class GraphImpl[VD: ClassTag, ED: ClassTag] protected (
     replicatedVertexView.edges.checkpoint()
   }
 
+  override def isCheckpointed: Boolean = {
+    vertices.isCheckpointed && replicatedVertexView.edges.isCheckpointed
+  }
+
+  override def getCheckpointFiles: Seq[String] = {
+    Seq(vertices.getCheckpointFile, replicatedVertexView.edges.getCheckpointFile).flatMap {
+      case Some(path) => Seq(path)
+      case None => Seq()
+    }
+  }
+
   override def unpersist(blocking: Boolean = true): Graph[VD, ED] = {
     unpersistVertices(blocking)
     replicatedVertexView.edges.unpersist(blocking)

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

@@ -74,7 +74,15 @@ class VertexRDDImpl[VD] private[graphx] (
   override def checkpoint() = {
     partitionsRDD.checkpoint()
   }
-    
+
+  override def isCheckpointed: Boolean = {
+    firstParent[ShippableVertexPartition[VD]].isCheckpointed
+  }
+
+  override def getCheckpointFile: Option[String] = {
+    partitionsRDD.getCheckpointFile
+  }
+
   /** The number of vertices in the RDD. */
   override def count(): Long = {
     partitionsRDD.map(_.size).reduce(_ + _)

graphx/src/test/scala/org/apache/spark/graphx/GraphSuite.scala

@@ -375,6 +375,8 @@ class GraphSuite extends FunSuite with LocalSparkContext {
       val ring = (0L to 100L).zip((1L to 99L) :+ 0L).map { case (a, b) => Edge(a, b, 1)}
       val rdd = sc.parallelize(ring)
       val graph = Graph.fromEdges(rdd, 1.0F)
+      assert(!graph.isCheckpointed)
+      assert(graph.getCheckpointFiles.size === 0)
       graph.checkpoint()
       graph.edges.map(_.attr).count()
       graph.vertices.map(_._2).count()
@@ -383,6 +385,8 @@ class GraphSuite extends FunSuite with LocalSparkContext {
       val verticesDependencies = graph.vertices.partitionsRDD.dependencies
       assert(edgesDependencies.forall(_.rdd.isInstanceOf[CheckpointRDD[_]]))
       assert(verticesDependencies.forall(_.rdd.isInstanceOf[CheckpointRDD[_]]))
+      assert(graph.isCheckpointed)
+      assert(graph.getCheckpointFiles.size === 2)
     }
   }
 

project/MimaExcludes.scala

@@ -127,6 +127,12 @@ object MimaExcludes {
             // SPARK-5315 Spark Streaming Java API returns Scala DStream
             ProblemFilters.exclude[MissingMethodProblem](
               "org.apache.spark.streaming.api.java.JavaDStreamLike.reduceByWindow")
+          ) ++ Seq(
+            // SPARK-5461 Graph should have isCheckpointed, getCheckpointFiles methods
+            ProblemFilters.exclude[MissingMethodProblem](
+              "org.apache.spark.graphx.Graph.getCheckpointFiles"),
+            ProblemFilters.exclude[MissingMethodProblem](
+              "org.apache.spark.graphx.Graph.isCheckpointed")
           )
 
         case v if v.startsWith("1.2") =>