More work on new RDD design

16 files changed, 476 insertions, 327 deletions

diff --git a/core/src/main/scala/spark/Aggregator.scala b/core/src/main/scala/spark/Aggregator.scala
new file mode 100644
index 0000000000..87453c9c15
--- /dev/null
+++ b/core/src/main/scala/spark/Aggregator.scala
@@ -0,0 +1,8 @@
+package spark
+
+@serializable
+class Aggregator[K, V, C] (
+  val createCombiner: V => C,
+  val mergeValue: (C, V) => C,
+  val mergeCombiners: (C, C) => C
+)
\ No newline at end of file
diff --git a/core/src/main/scala/spark/CartesianRDD.scala b/core/src/main/scala/spark/CartesianRDD.scala
new file mode 100644
index 0000000000..42a9b3b23c
--- /dev/null
+++ b/core/src/main/scala/spark/CartesianRDD.scala
@@ -0,0 +1,44 @@
+package spark
+
+@serializable class CartesianSplit(idx: Int, val s1: Split, val s2: Split)
+extends Split {
+  override val index = idx
+}
+
+@serializable
+class CartesianRDD[T: ClassManifest, U:ClassManifest](
+  sc: SparkContext, rdd1: RDD[T], rdd2: RDD[U])
+extends RDD[Pair[T, U]](sc) {
+  val numSplitsInRdd2 = rdd2.splits.size
+  
+  @transient val splits_ = {
+    // create the cross product split
+    val array = new Array[Split](rdd1.splits.size * rdd2.splits.size)
+    for (s1 <- rdd1.splits; s2 <- rdd2.splits) {
+      val idx = s1.index * numSplitsInRdd2 + s2.index
+      array(idx) = new CartesianSplit(idx, s1, s2)
+    }
+    array
+  }
+
+  override def splits = splits_.asInstanceOf[Array[Split]]
+
+  override def preferredLocations(split: Split) = {
+    val currSplit = split.asInstanceOf[CartesianSplit]
+    rdd1.preferredLocations(currSplit.s1) ++ rdd2.preferredLocations(currSplit.s2)
+  }
+
+  override def compute(split: Split) = {
+    val currSplit = split.asInstanceOf[CartesianSplit]
+    for (x <- rdd1.iterator(currSplit.s1); y <- rdd2.iterator(currSplit.s2)) yield (x, y)
+  }
+  
+  override val dependencies = List(
+    new NarrowDependency(rdd1) {
+      def getParents(id: Int): Seq[Int] = List(id / numSplitsInRdd2)
+    },
+    new NarrowDependency(rdd2) {
+      def getParents(id: Int): Seq[Int] = List(id % numSplitsInRdd2)
+    }
+  )
+}
\ No newline at end of file
diff --git a/core/src/main/scala/spark/Dependency.scala b/core/src/main/scala/spark/Dependency.scala
new file mode 100644
index 0000000000..20b0357e44
--- /dev/null
+++ b/core/src/main/scala/spark/Dependency.scala
@@ -0,0 +1,30 @@
+package spark
+
+@serializable
+abstract class Dependency[T](val rdd: RDD[T], val isShuffle: Boolean)
+
+abstract class NarrowDependency[T](rdd: RDD[T])
+extends Dependency(rdd, false) {
+  def getParents(outputPartition: Int): Seq[Int]
+}
+
+class ShuffleDependency[K, V, C](
+  val shuffleId: Int,
+  rdd: RDD[(K, V)],
+  val aggregator: Aggregator[K, V, C],
+  val partitioner: Partitioner[K]
+) extends Dependency(rdd, true)
+
+class OneToOneDependency[T](rdd: RDD[T]) extends NarrowDependency[T](rdd) {
+  override def getParents(partitionId: Int) = List(partitionId)
+}
+
+class RangeDependency[T](rdd: RDD[T], inStart: Int, outStart: Int, length: Int)
+extends NarrowDependency[T](rdd) {
+  override def getParents(partitionId: Int) = {
+    if (partitionId >= outStart && partitionId < outStart + length)
+      List(partitionId - outStart + inStart)
+    else
+      Nil
+  }
+}
diff --git a/core/src/main/scala/spark/Executor.scala b/core/src/main/scala/spark/Executor.scala
index b4d023b428..35469aeb3f 100644
--- a/core/src/main/scala/spark/Executor.scala
+++ b/core/src/main/scala/spark/Executor.scala
@@ -25,6 +25,8 @@ class Executor extends mesos.Executor with Logging {
     // Initialize cache and broadcast system (uses some properties read above)
     Cache.initialize()
     Broadcast.initialize(false)
+    MapOutputTracker.initialize(false)
+    RDDCache.initialize(false)
     
     // Create our ClassLoader (using spark properties) and set it on this thread
     classLoader = createClassLoader()
diff --git a/core/src/main/scala/spark/HadoopFile.scala b/core/src/main/scala/spark/HadoopFile.scala
index 629dcc7da5..754466204b 100644
--- a/core/src/main/scala/spark/HadoopFile.scala
+++ b/core/src/main/scala/spark/HadoopFile.scala
@@ -14,12 +14,13 @@ import org.apache.hadoop.mapred.Reporter
 import org.apache.hadoop.util.ReflectionUtils
 
 /** A Spark split class that wraps around a Hadoop InputSplit */
-@serializable class HadoopSplit(@transient s: InputSplit)
+@serializable class HadoopSplit(rddId: Int, idx: Int, @transient s: InputSplit)
 extends Split {
   val inputSplit = new SerializableWritable[InputSplit](s)
 
-  // Hadoop gives each split a unique toString value, so use this as our ID
-  override def getId() = "HadoopSplit(" + inputSplit.toString + ")"
+  override def hashCode(): Int = (41 * (41 + rddId) + idx).toInt
+
+  override val index = idx
 }
 
 
@@ -39,7 +40,10 @@ extends RDD[(K, V)](sc) {
     FileInputFormat.setInputPaths(conf, path)
     val inputFormat = createInputFormat(conf)
     val inputSplits = inputFormat.getSplits(conf, sc.numCores)
-    inputSplits.map(x => new HadoopSplit(x): Split).toArray
+    val array = new Array[Split] (inputSplits.size)
+    for (i <- 0 until inputSplits.size)
+      array(i) = new HadoopSplit(id, i, inputSplits(i))
+    array
   }
 
   def createInputFormat(conf: JobConf): InputFormat[K, V] = {
@@ -49,7 +53,7 @@ extends RDD[(K, V)](sc) {
 
   override def splits = splits_
 
-  override def iterator(theSplit: Split) = new Iterator[(K, V)] {
+  override def compute(theSplit: Split) = new Iterator[(K, V)] {
     val split = theSplit.asInstanceOf[HadoopSplit]
     var reader: RecordReader[K, V] = null
 
@@ -99,6 +103,8 @@ extends RDD[(K, V)](sc) {
     val hadoopSplit = split.asInstanceOf[HadoopSplit]
     hadoopSplit.inputSplit.value.getLocations.filter(_ != "localhost")
   }
+  
+  override val dependencies: List[Dependency[_]] = Nil
 }
 
 
diff --git a/core/src/main/scala/spark/MapOutputTracker.scala b/core/src/main/scala/spark/MapOutputTracker.scala
index 2c487cb627..ac62c6e411 100644
--- a/core/src/main/scala/spark/MapOutputTracker.scala
+++ b/core/src/main/scala/spark/MapOutputTracker.scala
@@ -2,7 +2,34 @@ package spark
 
 import java.util.concurrent.ConcurrentHashMap
 
+import scala.actors._
+import scala.actors.Actor._
+import scala.actors.remote._
+
+class MapOutputTracker extends DaemonActor with Logging {
+  def act() {
+    val port = System.getProperty("spark.master.port", "50501").toInt
+    RemoteActor.alive(port)
+    RemoteActor.register('MapOutputTracker, self)
+    logInfo("Started on port " + port)
+  }
+}
+
 object MapOutputTracker {
+  var trackerActor: AbstractActor = null
+  
+  def initialize(isMaster: Boolean) {
+    if (isMaster) {
+      val tracker = new MapOutputTracker
+      tracker.start
+      trackerActor = tracker
+    } else {
+      val host = System.getProperty("spark.master.host")
+      val port = System.getProperty("spark.master.port").toInt
+      trackerActor = RemoteActor.select(Node(host, port), 'MapOutputTracker)
+    }
+  }
+  
   private val serverUris = new ConcurrentHashMap[Int, Array[String]]
   
   def registerMapOutput(shuffleId: Int, numMaps: Int, mapId: Int, serverUri: String) {
diff --git a/core/src/main/scala/spark/ParallelArray.scala b/core/src/main/scala/spark/ParallelArray.scala
index a01904d61c..e77bc3014f 100644
--- a/core/src/main/scala/spark/ParallelArray.scala
+++ b/core/src/main/scala/spark/ParallelArray.scala
@@ -17,8 +17,7 @@ extends Split {
     case _ => false
   }
 
-  override def getId() =
-    "ParallelArraySplit(arrayId %d, slice %d)".format(arrayId, slice)
+  override val index = slice
 }
 
 class ParallelArray[T: ClassManifest](
@@ -28,8 +27,6 @@ extends RDD[T](sc) {
   // the RDD chain it gets cached. It might be worthwhile to write the data to
   // a file in the DFS and read it in the split instead.
 
-  val id = ParallelArray.newId()
-
   @transient val splits_ = {
     val slices = ParallelArray.slice(data, numSlices).toArray
     slices.indices.map(i => new ParallelArraySplit(id, i, slices(i))).toArray
@@ -37,9 +34,11 @@ extends RDD[T](sc) {
 
   override def splits = splits_.asInstanceOf[Array[Split]]
 
-  override def iterator(s: Split) = s.asInstanceOf[ParallelArraySplit[T]].iterator
+  override def compute(s: Split) = s.asInstanceOf[ParallelArraySplit[T]].iterator
   
   override def preferredLocations(s: Split): Seq[String] = Nil
+  
+  override val dependencies: List[Dependency[_]] = Nil
 }
 
 private object ParallelArray {
diff --git a/core/src/main/scala/spark/Partitioner.scala b/core/src/main/scala/spark/Partitioner.scala
new file mode 100644
index 0000000000..cc1ca74447
--- /dev/null
+++ b/core/src/main/scala/spark/Partitioner.scala
@@ -0,0 +1,22 @@
+package spark
+
+@serializable
+abstract class Partitioner[K] {
+  def numPartitions: Int
+  def getPartition(key: K): Int
+}
+
+class HashPartitioner[K](partitions: Int) extends Partitioner[K] {
+  def numPartitions = partitions
+
+  def getPartition(key: K) = {
+    val mod = key.hashCode % partitions
+    if (mod < 0) mod + partitions else mod // Guard against negative hash codes
+  }
+  
+  override def equals(other: Any): Boolean = other match {
+    case h: HashPartitioner[_] =>
+      h.numPartitions == numPartitions
+    case _ => false
+  }
+}
\ No newline at end of file
diff --git a/core/src/main/scala/spark/RDD.scala b/core/src/main/scala/spark/RDD.scala
index 9b650427c8..df044bd6cf 100644
--- a/core/src/main/scala/spark/RDD.scala
+++ b/core/src/main/scala/spark/RDD.scala
@@ -16,84 +16,78 @@ import SparkContext._
 import mesos._
 
 @serializable
-abstract class Dependency[T](val rdd: RDD[T], val isShuffle: Boolean)
-
-abstract class NarrowDependency[T](rdd: RDD[T])
-extends Dependency(rdd, false) {
-  def getParents(outputPartition: Int): Seq[Int]
-}
-
-class OneToOneDependency[T](rdd: RDD[T]) extends NarrowDependency[T](rdd) {
-  override def getParents(partitionId: Int) = List(partitionId)
-}
-
-class ShuffleDependency[K, V, C](
-  val shuffleId: Int,
-  rdd: RDD[(K, V)],
-  val aggregator: Aggregator[K, V, C],
-  val partitioner: Partitioner[K]
-) extends Dependency(rdd, true)
-
-@serializable
-class Aggregator[K, V, C] (
-  val createCombiner: V => C,
-  val mergeValue: (C, V) => C,
-  val mergeCombiners: (C, C) => C
-)
-
-@serializable
-abstract class Partitioner[K] {
-  def numPartitions: Int
-  def getPartition(key: K): Int
-}
-
-class HashPartitioner[K](partitions: Int) extends Partitioner[K] {
-  def numPartitions = partitions
-
-  def getPartition(key: K) = {
-    val mod = key.hashCode % partitions
-    if (mod < 0) mod + partitions else mod   // Careful of negative hash codes
-  }
-}
-
-@serializable
 abstract class RDD[T: ClassManifest](@transient sc: SparkContext) {
+  // Methods that must be implemented by subclasses
   def splits: Array[Split]
-  def iterator(split: Split): Iterator[T]
+  def compute(split: Split): Iterator[T]
   def preferredLocations(split: Split): Seq[String]
+  val dependencies: List[Dependency[_]]
   
-  val dependencies: List[Dependency[_]] = Nil
+  // Optionally overridden by subclasses to specify how they are partitioned
   val partitioner: Option[Partitioner[_]] = None
-
-  def sparkContext = sc
-
+  
+  def context = sc
+  
+  // Get a unique ID for this RDD
+  val id = sc.newRddId()
+  
+  // Variables relating to caching
+  private var shouldCache = false
+  
+  // Change this RDD's caching
+  def cache(): RDD[T] = {
+    shouldCache = true
+    this
+  }
+  
+  // Read this RDD; will read from cache if applicable, or otherwise compute
+  final def iterator(split: Split): Iterator[T] = {
+    if (shouldCache) {
+      RDDCache.getOrCompute[T](this, split)
+    } else {
+      compute(split)
+    }
+  }
+  
+  // Transformations
+  
   def map[U: ClassManifest](f: T => U): RDD[U] = new MappedRDD(this, sc.clean(f))
   
   def flatMap[U: ClassManifest](f: T => Traversable[U]): RDD[U] =
     new FlatMappedRDD(this, sc.clean(f))
-
-  /*
+  
   def filter(f: T => Boolean): RDD[T] = new FilteredRDD(this, sc.clean(f))
 
-  def cache() = new CachedRDD(this)
-
   def sample(withReplacement: Boolean, frac: Double, seed: Int): RDD[T] =
     new SampledRDD(this, withReplacement, frac, seed)
 
+  def union(other: RDD[T]): RDD[T] = new UnionRDD(sc, Array(this, other))
+
+  def ++(other: RDD[T]): RDD[T] = this.union(other)
+
+  def glom(): RDD[Array[T]] = new SplitRDD(this)
+
+  def cartesian[U: ClassManifest](other: RDD[U]): RDD[(T, U)] =
+    new CartesianRDD(sc, this, other)
+
+  def groupBy[K](func: T => K, numSplits: Int): RDD[(K, Seq[T])] =
+    this.map(t => (func(t), t)).groupByKey(numSplits)
+
+  def groupBy[K](func: T => K): RDD[(K, Seq[T])] =
+    groupBy[K](func, sc.numCores)
+
+  // Parallel operations
+  
   def foreach(f: T => Unit) {
     val cleanF = sc.clean(f)
-    val tasks = splits.map(s => new ForeachTask(this, s, cleanF)).toArray
-    sc.runTaskObjects(tasks)
+    sc.runJob(this, (iter: Iterator[T]) => iter.foreach(cleanF))
   }
-  */
 
   def collect(): Array[T] = {
     val results = sc.runJob(this, (iter: Iterator[T]) => iter.toArray)
     Array.concat(results: _*)
   }
 
-  def toArray(): Array[T] = collect()
-
   def reduce(f: (T, T) => T): T = {
     val cleanF = sc.clean(f)
     val reducePartition: Iterator[T] => Option[T] = iter => {
@@ -111,7 +105,15 @@ abstract class RDD[T: ClassManifest](@transient sc: SparkContext) {
     else
       return results.reduceLeft(f)
   }
+  
+  def count(): Long = {
+    sc.runJob(this, (iter: Iterator[T]) => iter.size.toLong).sum
+  }
+
+  def toArray(): Array[T] = collect()
 
+  // TODO: Reimplement these to properly build any shuffle dependencies on
+  // the cluster rather than attempting to compute a partiton on the master
   /*
   def take(num: Int): Array[T] = {
     if (num == 0)
@@ -130,279 +132,43 @@ abstract class RDD[T: ClassManifest](@transient sc: SparkContext) {
     case _ => throw new UnsupportedOperationException("empty collection")
   }
   */
-
-  def count(): Long = {
-    try {
-      map(x => 1L).reduce(_+_) 
-    } catch { 
-      case e: UnsupportedOperationException => 0L // No elements in RDD
-    }
-  }
-
-  def union(other: RDD[T]): RDD[T] = new UnionRDD(sc, Array(this, other))
-
-  def ++(other: RDD[T]): RDD[T] = this.union(other)
-
-  //def splitRdd(): RDD[Array[T]] = new SplitRDD(this)
-
-  //def cartesian[U: ClassManifest](other: RDD[U]): RDD[(T, U)] =
-  //  new CartesianRDD(sc, this, other)
-
-  def groupBy[K](func: T => K, numSplits: Int): RDD[(K, Seq[T])] =
-    this.map(t => (func(t), t)).groupByKey(numSplits)
-
-  def groupBy[K](func: T => K): RDD[(K, Seq[T])] =
-    groupBy[K](func, sc.numCores)
 }
 
 class MappedRDD[U: ClassManifest, T: ClassManifest](
   prev: RDD[T], f: T => U)
-extends RDD[U](prev.sparkContext) {
+extends RDD[U](prev.context) {
   override def splits = prev.splits
   override def preferredLocations(split: Split) = prev.preferredLocations(split)
   override val dependencies = List(new OneToOneDependency(prev))
-  override def iterator(split: Split) = prev.iterator(split).map(f)
+  override def compute(split: Split) = prev.iterator(split).map(f)
 }
 
 class FlatMappedRDD[U: ClassManifest, T: ClassManifest](
   prev: RDD[T], f: T => Traversable[U])
-extends RDD[U](prev.sparkContext) {
+extends RDD[U](prev.context) {
   override def splits = prev.splits
   override def preferredLocations(split: Split) = prev.preferredLocations(split)
   override val dependencies = List(new OneToOneDependency(prev))
-  override def iterator(split: Split) = prev.iterator(split).toStream.flatMap(f).iterator
+  override def compute(split: Split) = prev.iterator(split).toStream.flatMap(f).iterator
 }
 
-/*
 class FilteredRDD[T: ClassManifest](
   prev: RDD[T], f: T => Boolean)
-extends RDD[T](prev.sparkContext) {
+extends RDD[T](prev.context) {
   override def splits = prev.splits
   override def preferredLocations(split: Split) = prev.preferredLocations(split)
-  override def iterator(split: Split) = prev.iterator(split).filter(f)
+  override val dependencies = List(new OneToOneDependency(prev))
+  override def compute(split: Split) = prev.iterator(split).filter(f)
 }
 
 class SplitRDD[T: ClassManifest](prev: RDD[T])
-extends RDD[Array[T]](prev.sparkContext) {
+extends RDD[Array[T]](prev.context) {
   override def splits = prev.splits
   override def preferredLocations(split: Split) = prev.preferredLocations(split)
-  override def iterator(split: Split) = Iterator.fromArray(Array(prev.iterator(split).toArray))
-}
-
-
-@serializable class SeededSplit(val prev: Split, val seed: Int) extends Split {
-  override def getId() =
-    "SeededSplit(" + prev.getId() + ", seed " + seed + ")"
-}
-
-class SampledRDD[T: ClassManifest](
-  prev: RDD[T], withReplacement: Boolean, frac: Double, seed: Int)
-extends RDD[T](prev.sparkContext) {
-
-  @transient val splits_ = { val rg = new Random(seed); prev.splits.map(x => new SeededSplit(x, rg.nextInt)) }
-
-  override def splits = splits_.asInstanceOf[Array[Split]]
-
-  override def preferredLocations(split: Split) = prev.preferredLocations(split.asInstanceOf[SeededSplit].prev)
-
-  override def iterator(splitIn: Split) = {
-    val split = splitIn.asInstanceOf[SeededSplit]
-    val rg = new Random(split.seed);
-    // Sampling with replacement (TODO: use reservoir sampling to make this more efficient?)
-    if (withReplacement) {
-      val oldData = prev.iterator(split.prev).toArray
-      val sampleSize = (oldData.size * frac).ceil.toInt
-      val sampledData = for (i <- 1 to sampleSize) yield oldData(rg.nextInt(oldData.size)) // all of oldData's indices are candidates, even if sampleSize < oldData.size
-      sampledData.iterator
-    }
-    // Sampling without replacement
-    else {
-      prev.iterator(split.prev).filter(x => (rg.nextDouble <= frac))
-    }
-  }
-}
-
-
-class CachedRDD[T](
-  prev: RDD[T])(implicit m: ClassManifest[T])
-extends RDD[T](prev.sparkContext) with Logging {
-  val id = CachedRDD.newId()
-  @transient val cacheLocs = Map[Split, List[String]]()
-
-  override def splits = prev.splits
-
-  override def preferredLocations(split: Split) = {
-    if (cacheLocs.contains(split))
-      cacheLocs(split)
-    else
-      prev.preferredLocations(split)
-  }
-
-  override def iterator(split: Split): Iterator[T] = {
-    val key = id + "::" + split.getId()
-    logInfo("CachedRDD split key is " + key)
-    val cache = CachedRDD.cache
-    val loading = CachedRDD.loading
-    val cachedVal = cache.get(key)
-    if (cachedVal != null) {
-      // Split is in cache, so just return its values
-      return Iterator.fromArray(cachedVal.asInstanceOf[Array[T]])
-    } else {
-      // Mark the split as loading (unless someone else marks it first)
-      loading.synchronized {
-        if (loading.contains(key)) {
-          while (loading.contains(key)) {
-            try {loading.wait()} catch {case _ =>}
-          }
-          return Iterator.fromArray(cache.get(key).asInstanceOf[Array[T]])
-        } else {
-          loading.add(key)
-        }
-      }
-      // If we got here, we have to load the split
-      logInfo("Loading and caching " + split)
-      val array = prev.iterator(split).toArray(m)
-      cache.put(key, array)
-      loading.synchronized {
-        loading.remove(key)
-        loading.notifyAll()
-      }
-      return Iterator.fromArray(array)
-    }
-  }
-
-  override def taskStarted(split: Split, slot: SlaveOffer) {
-    val oldList = cacheLocs.getOrElse(split, Nil)
-    val host = slot.getHost
-    if (!oldList.contains(host))
-      cacheLocs(split) = host :: oldList
-  }
-}
-
-private object CachedRDD {
-  val nextId = new AtomicLong(0) // Generates IDs for cached RDDs (on master)
-  def newId() = nextId.getAndIncrement()
-
-  // Stores map results for various splits locally (on workers)
-  val cache = Cache.newKeySpace()
-
-  // Remembers which splits are currently being loaded (on workers)
-  val loading = new HashSet[String]
-}
-*/
-
-@serializable
-class UnionSplit[T: ClassManifest](rdd: RDD[T], index: Int, split: Split)
-extends Split {
-  def iterator() = rdd.iterator(split)
-  def preferredLocations() = rdd.preferredLocations(split)
-  override def getId() = "UnionSplit(" + index + ", " + split.getId() + ")"
-}
-
-@serializable
-class UnionRDD[T: ClassManifest](sc: SparkContext, rdds: Seq[RDD[T]])
-extends RDD[T](sc) {
-  @transient val splits_ : Array[Split] = {
-    val splits: Seq[Split] =
-      for ((rdd, index) <- rdds.zipWithIndex; split <- rdd.splits)
-        yield new UnionSplit(rdd, index, split)
-    splits.toArray
-  }
-
-  override def splits = splits_
-
-  override def iterator(s: Split): Iterator[T] =
-    s.asInstanceOf[UnionSplit[T]].iterator()
-
-  override def preferredLocations(s: Split): Seq[String] =
-    s.asInstanceOf[UnionSplit[T]].preferredLocations()
-}
-
-/*
-@serializable class CartesianSplit(val s1: Split, val s2: Split) extends Split {
-  override def getId() =
-    "CartesianSplit(" + s1.getId() + ", " + s2.getId() + ")"
-}
-
-@serializable
-class CartesianRDD[T: ClassManifest, U:ClassManifest](
-  sc: SparkContext, rdd1: RDD[T], rdd2: RDD[U])
-extends RDD[Pair[T, U]](sc) {
-  @transient val splits_ = {
-    // create the cross product split
-    rdd2.splits.map(y => rdd1.splits.map(x => new CartesianSplit(x, y))).flatten
-  }
-
-  override def splits = splits_.asInstanceOf[Array[Split]]
-
-  override def preferredLocations(split: Split) = {
-    val currSplit = split.asInstanceOf[CartesianSplit]
-    rdd1.preferredLocations(currSplit.s1) ++ rdd2.preferredLocations(currSplit.s2)
-  }
-
-  override def iterator(split: Split) = {
-    val currSplit = split.asInstanceOf[CartesianSplit]
-    for (x <- rdd1.iterator(currSplit.s1); y <- rdd2.iterator(currSplit.s2)) yield (x, y)
-  }
-
-  override def taskStarted(split: Split, slot: SlaveOffer) = {
-    val currSplit = split.asInstanceOf[CartesianSplit]
-    rdd1.taskStarted(currSplit.s1, slot)
-    rdd2.taskStarted(currSplit.s2, slot)
-  }
-}
-*/
-
-class ShuffledRDDSplit(val id: Int) extends Split {
-  override def getId() = "ShuffleRDDSplit(" + id + ")"
+  override val dependencies = List(new OneToOneDependency(prev))
+  override def compute(split: Split) = Iterator.fromArray(Array(prev.iterator(split).toArray))
 }
 
-class ShuffledRDD[K, V, C](
-  parent: RDD[(K, V)],
-  aggregator: Aggregator[K, V, C],
-  partitioner: Partitioner[K])
-extends RDD[(K, C)](parent.sparkContext) {
-  @transient val splits_ =
-    Array.tabulate[Split](partitioner.numPartitions)(i => new ShuffledRDDSplit(i))
-  
-  val dep = new ShuffleDependency(sparkContext.newShuffleId, parent, aggregator, partitioner)
-
-  override def splits = splits_
-
-  override def preferredLocations(split: Split) = Nil
-
-  override def iterator(split: Split): Iterator[(K, C)] = {
-    val shuffleId = dep.shuffleId
-    val splitId = split.asInstanceOf[ShuffledRDDSplit].id
-    val splitsByUri = new HashMap[String, ArrayBuffer[Int]]
-    val serverUris = MapOutputTracker.getServerUris(shuffleId)
-    for ((serverUri, index) <- serverUris.zipWithIndex) {
-      splitsByUri.getOrElseUpdate(serverUri, ArrayBuffer()) += index
-    }
-    val combiners = new HashMap[K, C]
-    for ((serverUri, inputIds) <- Utils.shuffle(splitsByUri)) {
-      for (i <- inputIds) {
-        val url = "%s/shuffle/%d/%d/%d".format(serverUri, shuffleId, i, splitId)
-        val inputStream = new ObjectInputStream(new URL(url).openStream())
-        try {
-          while (true) {
-            val (k, c) = inputStream.readObject().asInstanceOf[(K, C)]
-            combiners(k) = combiners.get(k) match {
-              case Some(oldC) => aggregator.mergeCombiners(oldC, c)
-              case None => c
-            }
-          }
-        } catch {
-          case e: EOFException => {}
-        }
-        inputStream.close()
-      }
-    }
-    combiners.iterator
-  }
-
-  override val dependencies = List(dep)
-}
 
 @serializable class PairRDDExtras[K, V](self: RDD[(K, V)]) {
   def reduceByKeyToDriver(func: (V, V) => V): Map[K, V] = {
@@ -427,13 +193,6 @@ extends RDD[(K, C)](parent.sparkContext) {
     val aggregator = new Aggregator[K, V, C](createCombiner, mergeValue, mergeCombiners)
     val partitioner = new HashPartitioner[K](numSplits)
     new ShuffledRDD(self, aggregator, partitioner)
-    // TODO
-    /*
-    val shufClass = Class.forName(System.getProperty(
-      "spark.shuffle.class", "spark.LocalFileShuffle"))
-    val shuf = shufClass.newInstance().asInstanceOf[Shuffle[K, V, C]]
-    shuf.compute(self, numSplits, createCombiner, mergeValue, mergeCombiners)
-    */
   }
 
   def reduceByKey(func: (V, V) => V, numSplits: Int): RDD[(K, V)] = {
@@ -484,7 +243,7 @@ extends RDD[(K, C)](parent.sparkContext) {
     join(other, numCores)
   }
 
-  def numCores = self.sparkContext.numCores
+  def numCores = self.context.numCores
 
   def collectAsMap(): Map[K, V] = HashMap(self.collect(): _*)
 }
diff --git a/core/src/main/scala/spark/RDDCache.scala b/core/src/main/scala/spark/RDDCache.scala
new file mode 100644
index 0000000000..2f2ec9d237
--- /dev/null
+++ b/core/src/main/scala/spark/RDDCache.scala
@@ -0,0 +1,92 @@
+package spark
+
+import scala.actors._
+import scala.actors.Actor._
+import scala.actors.remote._
+
+sealed trait CacheMessage
+case class CacheEntryAdded(rddId: Int, partition: Int, host: String)
+case class CacheEntryRemoved(rddId: Int, partition: Int, host: String)
+
+class RDDCacheTracker extends DaemonActor with Logging {
+  def act() {
+    val port = System.getProperty("spark.master.port", "50501").toInt
+    RemoteActor.alive(port)
+    RemoteActor.register('RDDCacheTracker, self)
+    logInfo("Started on port " + port)
+    
+    loop {
+      react {
+        case CacheEntryAdded(rddId, partition, host) =>
+          logInfo("Cache entry added: %s, %s, %s".format(rddId, partition, host))
+          
+        case CacheEntryRemoved(rddId, partition, host) =>
+          logInfo("Cache entry removed: %s, %s, %s".format(rddId, partition, host))
+      }
+    }
+  }
+}
+
+import scala.collection.mutable.HashSet
+private object RDDCache extends Logging {
+  // Stores map results for various splits locally
+  val cache = Cache.newKeySpace()
+
+  // Remembers which splits are currently being loaded
+  val loading = new HashSet[(Int, Int)]
+  
+  // Tracker actor on the master, or remote reference to it on workers
+  var trackerActor: AbstractActor = null
+  
+  def initialize(isMaster: Boolean) {
+    if (isMaster) {
+      val tracker = new RDDCacheTracker
+      tracker.start
+      trackerActor = tracker
+    } else {
+      val host = System.getProperty("spark.master.host")
+      val port = System.getProperty("spark.master.port").toInt
+      trackerActor = RemoteActor.select(Node(host, port), 'RDDCacheTracker)
+    }
+  }
+  
+  // Gets or computes an RDD split
+  def getOrCompute[T](rdd: RDD[T], split: Split)(implicit m: ClassManifest[T])
+      : Iterator[T] = {
+    val key = (rdd.id, split.index)
+    logInfo("CachedRDD split key is " + key)
+    val cache = RDDCache.cache
+    val loading = RDDCache.loading
+    val cachedVal = cache.get(key)
+    if (cachedVal != null) {
+      // Split is in cache, so just return its values
+      return Iterator.fromArray(cachedVal.asInstanceOf[Array[T]])
+    } else {
+      // Mark the split as loading (unless someone else marks it first)
+      loading.synchronized {
+        if (loading.contains(key)) {
+          while (loading.contains(key)) {
+            try {loading.wait()} catch {case _ =>}
+          }
+          return Iterator.fromArray(cache.get(key).asInstanceOf[Array[T]])
+        } else {
+          loading.add(key)
+        }
+      }
+      val host = System.getProperty("spark.hostname", Utils.localHostName)
+      trackerActor ! CacheEntryAdded(rdd.id, split.index, host)
+      // If we got here, we have to load the split
+      // TODO: fetch any remote copy of the split that may be available
+      // TODO: also notify the master that we're loading it
+      // TODO: also register a listener for when it unloads
+      logInfo("Computing and caching " + split)
+      val array = rdd.compute(split).toArray(m)
+      cache.put(key, array)
+      loading.synchronized {
+        loading.remove(key)
+        loading.notifyAll()
+      }
+      return Iterator.fromArray(array)
+    }
+  }
+}
\ No newline at end of file
diff --git a/core/src/main/scala/spark/SampledRDD.scala b/core/src/main/scala/spark/SampledRDD.scala
new file mode 100644
index 0000000000..2eeafedcdd
--- /dev/null
+++ b/core/src/main/scala/spark/SampledRDD.scala
@@ -0,0 +1,36 @@
+package spark
+
+import java.util.Random
+
+@serializable class SampledRDDSplit(val prev: Split, val seed: Int) extends Split {
+  override val index = prev.index
+}
+
+class SampledRDD[T: ClassManifest](
+  prev: RDD[T], withReplacement: Boolean, frac: Double, seed: Int)
+extends RDD[T](prev.context) {
+
+  @transient val splits_ = { val rg = new Random(seed); prev.splits.map(x => new SampledRDDSplit(x, rg.nextInt)) }
+
+  override def splits = splits_.asInstanceOf[Array[Split]]
+
+  override val dependencies = List(new OneToOneDependency(prev))
+  
+  override def preferredLocations(split: Split) = prev.preferredLocations(split.asInstanceOf[SampledRDDSplit].prev)
+
+  override def compute(splitIn: Split) = {
+    val split = splitIn.asInstanceOf[SampledRDDSplit]
+    val rg = new Random(split.seed);
+    // Sampling with replacement (TODO: use reservoir sampling to make this more efficient?)
+    if (withReplacement) {
+      val oldData = prev.iterator(split.prev).toArray
+      val sampleSize = (oldData.size * frac).ceil.toInt
+      val sampledData = for (i <- 1 to sampleSize) yield oldData(rg.nextInt(oldData.size)) // all of oldData's indices are candidates, even if sampleSize < oldData.size
+      sampledData.iterator
+    }
+    // Sampling without replacement
+    else {
+      prev.iterator(split.prev).filter(x => (rg.nextDouble <= frac))
+    }
+  }
+}
diff --git a/core/src/main/scala/spark/ShuffledRDD.scala b/core/src/main/scala/spark/ShuffledRDD.scala
new file mode 100644
index 0000000000..826957a469
--- /dev/null
+++ b/core/src/main/scala/spark/ShuffledRDD.scala
@@ -0,0 +1,60 @@
+package spark
+
+import java.net.URL
+import java.io.EOFException
+import java.io.ObjectInputStream
+import scala.collection.mutable.ArrayBuffer
+import scala.collection.mutable.HashMap
+
+class ShuffledRDDSplit(val idx: Int) extends Split {
+  override val index = idx
+  override def hashCode(): Int = idx
+}
+
+class ShuffledRDD[K, V, C](
+  parent: RDD[(K, V)],
+  aggregator: Aggregator[K, V, C],
+  part : Partitioner[K])
+extends RDD[(K, C)](parent.context) {
+  override val partitioner = Some(part)
+  
+  @transient val splits_ =
+    Array.tabulate[Split](part.numPartitions)(i => new ShuffledRDDSplit(i))
+
+  override def splits = splits_
+  
+  override def preferredLocations(split: Split) = Nil
+  
+  val dep = new ShuffleDependency(context.newShuffleId, parent, aggregator, part)
+  override val dependencies = List(dep)
+
+  override def compute(split: Split): Iterator[(K, C)] = {
+    val shuffleId = dep.shuffleId
+    val splitId = split.index
+    val splitsByUri = new HashMap[String, ArrayBuffer[Int]]
+    val serverUris = MapOutputTracker.getServerUris(shuffleId)
+    for ((serverUri, index) <- serverUris.zipWithIndex) {
+      splitsByUri.getOrElseUpdate(serverUri, ArrayBuffer()) += index
+    }
+    val combiners = new HashMap[K, C]
+    for ((serverUri, inputIds) <- Utils.shuffle(splitsByUri)) {
+      for (i <- inputIds) {
+        val url = "%s/shuffle/%d/%d/%d".format(serverUri, shuffleId, i, splitId)
+        val inputStream = new ObjectInputStream(new URL(url).openStream())
+        try {
+          while (true) {
+            val (k, c) = inputStream.readObject().asInstanceOf[(K, C)]
+            combiners(k) = combiners.get(k) match {
+              case Some(oldC) => aggregator.mergeCombiners(oldC, c)
+              case None => c
+            }
+          }
+        } catch {
+          case e: EOFException => {}
+        }
+        inputStream.close()
+      }
+    }
+    combiners.iterator
+  }
+}
\ No newline at end of file
diff --git a/core/src/main/scala/spark/SparkContext.scala b/core/src/main/scala/spark/SparkContext.scala
index b4799d7c08..fda2ee3be7 100644
--- a/core/src/main/scala/spark/SparkContext.scala
+++ b/core/src/main/scala/spark/SparkContext.scala
@@ -1,6 +1,7 @@
 package spark
 
 import java.io._
+import java.util.concurrent.atomic.AtomicInteger
 
 import scala.collection.mutable.ArrayBuffer
 
@@ -34,6 +35,8 @@ extends Logging {
   scheduler.start()
   Cache.initialize()
   Broadcast.initialize(true)
+  MapOutputTracker.initialize(true)
+  RDDCache.initialize(true)
 
   // Methods for creating RDDs
 
@@ -42,6 +45,12 @@ extends Logging {
 
   def parallelize[T: ClassManifest](seq: Seq[T]): RDD[T] =
     parallelize(seq, numCores)
+    
+  def makeRDD[T: ClassManifest](seq: Seq[T], numSlices: Int): RDD[T] =
+    parallelize(seq, numSlices)
+
+  def makeRDD[T: ClassManifest](seq: Seq[T]): RDD[T] =
+    parallelize(seq, numCores)
 
   def textFile(path: String): RDD[String] =
     new HadoopTextFile(this, path)
@@ -158,12 +167,16 @@ extends Logging {
   // Get the number of cores available to run tasks (as reported by Scheduler)
   def numCores = scheduler.numCores
 
-  private var nextShuffleId: Int = 0
+  private var nextShuffleId = new AtomicInteger(0)
 
   private[spark] def newShuffleId(): Int = {
-    val id = nextShuffleId
-    nextShuffleId += 1
-    id
+    nextShuffleId.getAndIncrement()
+  }
+  
+  private var nextRddId = new AtomicInteger(0)
+
+  private[spark] def newRddId(): Int = {
+    nextRddId.getAndIncrement()
   }
 }
 
diff --git a/core/src/main/scala/spark/Split.scala b/core/src/main/scala/spark/Split.scala
index 116cd16370..62bb5f82c5 100644
--- a/core/src/main/scala/spark/Split.scala
+++ b/core/src/main/scala/spark/Split.scala
@@ -5,9 +5,10 @@ package spark
  */
 @serializable trait Split {
   /**
-   * Get a unique ID for this split which can be used, for example, to
-   * set up caches based on it. The ID should stay the same if we serialize
-   * and then deserialize the split.
+   * Get the split's index within its parent RDD
    */
-  def getId(): String
+  val index: Int
+  
+  // A better default implementation of HashCode
+  override def hashCode(): Int = index
 }
diff --git a/core/src/main/scala/spark/UnionRDD.scala b/core/src/main/scala/spark/UnionRDD.scala
new file mode 100644
index 0000000000..78297be4f3
--- /dev/null
+++ b/core/src/main/scala/spark/UnionRDD.scala
@@ -0,0 +1,43 @@
+package spark
+
+import scala.collection.mutable.ArrayBuffer
+
+@serializable
+class UnionSplit[T: ClassManifest](idx: Int, rdd: RDD[T], split: Split)
+extends Split {
+  def iterator() = rdd.iterator(split)
+  def preferredLocations() = rdd.preferredLocations(split)
+  override val index = idx
+}
+
+@serializable
+class UnionRDD[T: ClassManifest](sc: SparkContext, rdds: Seq[RDD[T]])
+extends RDD[T](sc) {
+  @transient val splits_ : Array[Split] = {
+    val array = new Array[Split](rdds.map(_.splits.size).sum)
+    var pos = 0
+    for (rdd <- rdds; split <- rdd.splits) {
+      array(pos) = new UnionSplit(pos, rdd, split)
+      pos += 1
+    }
+    array
+  }
+
+  override def splits = splits_
+
+  override val dependencies = {
+    val deps = new ArrayBuffer[Dependency[_]]
+    var pos = 0
+    for ((rdd, index) <- rdds.zipWithIndex) {
+      deps += new RangeDependency(rdd, 0, pos, rdd.splits.size) 
+      pos += rdd.splits.size
+    }
+    deps.toList
+  }
+  
+  override def compute(s: Split): Iterator[T] =
+    s.asInstanceOf[UnionSplit[T]].iterator()
+
+  override def preferredLocations(s: Split): Seq[String] =
+    s.asInstanceOf[UnionSplit[T]].preferredLocations()
+}
\ No newline at end of file
diff --git a/core/src/main/scala/spark/Utils.scala b/core/src/main/scala/spark/Utils.scala
index e333dd9c91..00cbbfd616 100644
--- a/core/src/main/scala/spark/Utils.scala
+++ b/core/src/main/scala/spark/Utils.scala
@@ -124,4 +124,11 @@ object Utils {
     // and join them into a string
     return bytes.map(b => (b.toInt + 256) % 256).mkString(".")
   }
+
+  /**
+   * Get the local machine's hostname
+   */
+  def localHostName(): String = {
+    return InetAddress.getLocalHost().getHostName
+  }
 }