Merge pull request #359 from ScrapCodes/clone-writables

We clone hadoop key and values by default and reuse objects if asked to.

 We try to clone for most common types of writables and we call WritableUtils.clone otherwise intention is to optimize, for example for NullWritable there is no need and for Long, int and String creating a new object with value set would be faster than doing copy on object hopefully.

There is another way to do this PR where we ask for both key and values whether to clone them or not, but could not think of a use case for it except either of them is actually a NullWritable for which I have already worked around. So thought that would be unnecessary.

core/src/main/scala/org/apache/spark/SparkContext.scala

@@ -349,25 +349,27 @@ class SparkContext(
    * other necessary info (e.g. file name for a filesystem-based dataset, table name for HyperTable,
    * etc).
    */
-  def hadoopRDD[K, V](
+  def hadoopRDD[K: ClassTag, V: ClassTag](
       conf: JobConf,
       inputFormatClass: Class[_ <: InputFormat[K, V]],
       keyClass: Class[K],
       valueClass: Class[V],
-      minSplits: Int = defaultMinSplits
+      minSplits: Int = defaultMinSplits,
+      cloneKeyValues: Boolean = true
       ): RDD[(K, V)] = {
     // Add necessary security credentials to the JobConf before broadcasting it.
     SparkHadoopUtil.get.addCredentials(conf)
-    new HadoopRDD(this, conf, inputFormatClass, keyClass, valueClass, minSplits)
+    new HadoopRDD(this, conf, inputFormatClass, keyClass, valueClass, minSplits, cloneKeyValues)
   }
 
   /** Get an RDD for a Hadoop file with an arbitrary InputFormat */
-  def hadoopFile[K, V](
+  def hadoopFile[K: ClassTag, V: ClassTag](
       path: String,
       inputFormatClass: Class[_ <: InputFormat[K, V]],
       keyClass: Class[K],
       valueClass: Class[V],
-      minSplits: Int = defaultMinSplits
+      minSplits: Int = defaultMinSplits,
+      cloneKeyValues: Boolean = true
       ): RDD[(K, V)] = {
     // A Hadoop configuration can be about 10 KB, which is pretty big, so broadcast it.
     val confBroadcast = broadcast(new SerializableWritable(hadoopConfiguration))
@@ -379,7 +381,8 @@ class SparkContext(
       inputFormatClass,
       keyClass,
       valueClass,
-      minSplits)
+      minSplits,
+      cloneKeyValues)
   }
 
   /**
@@ -390,14 +393,15 @@ class SparkContext(
    * val file = sparkContext.hadoopFile[LongWritable, Text, TextInputFormat](path, minSplits)
    * }}}
    */
-  def hadoopFile[K, V, F <: InputFormat[K, V]](path: String, minSplits: Int)
-      (implicit km: ClassTag[K], vm: ClassTag[V], fm: ClassTag[F])
-      : RDD[(K, V)] = {
+  def hadoopFile[K, V, F <: InputFormat[K, V]]
+      (path: String, minSplits: Int, cloneKeyValues: Boolean = true)
+      (implicit km: ClassTag[K], vm: ClassTag[V], fm: ClassTag[F]): RDD[(K, V)] = {
     hadoopFile(path,
-        fm.runtimeClass.asInstanceOf[Class[F]],
-        km.runtimeClass.asInstanceOf[Class[K]],
-        vm.runtimeClass.asInstanceOf[Class[V]],
-        minSplits)
+      fm.runtimeClass.asInstanceOf[Class[F]],
+      km.runtimeClass.asInstanceOf[Class[K]],
+      vm.runtimeClass.asInstanceOf[Class[V]],
+      minSplits,
+      cloneKeyValues = cloneKeyValues)
   }
 
   /**
@@ -408,61 +412,67 @@ class SparkContext(
    * val file = sparkContext.hadoopFile[LongWritable, Text, TextInputFormat](path)
    * }}}
    */
-  def hadoopFile[K, V, F <: InputFormat[K, V]](path: String)
+  def hadoopFile[K, V, F <: InputFormat[K, V]](path: String, cloneKeyValues: Boolean = true)
       (implicit km: ClassTag[K], vm: ClassTag[V], fm: ClassTag[F]): RDD[(K, V)] =
-    hadoopFile[K, V, F](path, defaultMinSplits)
+    hadoopFile[K, V, F](path, defaultMinSplits, cloneKeyValues)
 
   /** Get an RDD for a Hadoop file with an arbitrary new API InputFormat. */
-  def newAPIHadoopFile[K, V, F <: NewInputFormat[K, V]](path: String)
+  def newAPIHadoopFile[K, V, F <: NewInputFormat[K, V]]
+      (path: String, cloneKeyValues: Boolean = true)
       (implicit km: ClassTag[K], vm: ClassTag[V], fm: ClassTag[F]): RDD[(K, V)] = {
     newAPIHadoopFile(
-        path,
-        fm.runtimeClass.asInstanceOf[Class[F]],
-        km.runtimeClass.asInstanceOf[Class[K]],
-        vm.runtimeClass.asInstanceOf[Class[V]])
+      path,
+      fm.runtimeClass.asInstanceOf[Class[F]],
+      km.runtimeClass.asInstanceOf[Class[K]],
+      vm.runtimeClass.asInstanceOf[Class[V]],
+      cloneKeyValues = cloneKeyValues)
   }
 
   /**
    * Get an RDD for a given Hadoop file with an arbitrary new API InputFormat
    * and extra configuration options to pass to the input format.
    */
-  def newAPIHadoopFile[K, V, F <: NewInputFormat[K, V]](
+  def newAPIHadoopFile[K: ClassTag, V: ClassTag, F <: NewInputFormat[K, V]](
       path: String,
       fClass: Class[F],
       kClass: Class[K],
       vClass: Class[V],
-      conf: Configuration = hadoopConfiguration): RDD[(K, V)] = {
+      conf: Configuration = hadoopConfiguration,
+      cloneKeyValues: Boolean = true): RDD[(K, V)] = {
     val job = new NewHadoopJob(conf)
     NewFileInputFormat.addInputPath(job, new Path(path))
     val updatedConf = job.getConfiguration
-    new NewHadoopRDD(this, fClass, kClass, vClass, updatedConf)
+    new NewHadoopRDD(this, fClass, kClass, vClass, updatedConf, cloneKeyValues)
   }
 
   /**
    * Get an RDD for a given Hadoop file with an arbitrary new API InputFormat
    * and extra configuration options to pass to the input format.
    */
-  def newAPIHadoopRDD[K, V, F <: NewInputFormat[K, V]](
+  def newAPIHadoopRDD[K: ClassTag, V: ClassTag, F <: NewInputFormat[K, V]](
       conf: Configuration = hadoopConfiguration,
       fClass: Class[F],
       kClass: Class[K],
-      vClass: Class[V]): RDD[(K, V)] = {
-    new NewHadoopRDD(this, fClass, kClass, vClass, conf)
+      vClass: Class[V],
+      cloneKeyValues: Boolean = true): RDD[(K, V)] = {
+    new NewHadoopRDD(this, fClass, kClass, vClass, conf, cloneKeyValues)
   }
 
   /** Get an RDD for a Hadoop SequenceFile with given key and value types. */
-  def sequenceFile[K, V](path: String,
+  def sequenceFile[K: ClassTag, V: ClassTag](path: String,
       keyClass: Class[K],
       valueClass: Class[V],
-      minSplits: Int
+      minSplits: Int,
+      cloneKeyValues: Boolean = true
       ): RDD[(K, V)] = {
     val inputFormatClass = classOf[SequenceFileInputFormat[K, V]]
-    hadoopFile(path, inputFormatClass, keyClass, valueClass, minSplits)
+    hadoopFile(path, inputFormatClass, keyClass, valueClass, minSplits, cloneKeyValues)
   }
 
   /** Get an RDD for a Hadoop SequenceFile with given key and value types. */
-  def sequenceFile[K, V](path: String, keyClass: Class[K], valueClass: Class[V]): RDD[(K, V)] =
-    sequenceFile(path, keyClass, valueClass, defaultMinSplits)
+  def sequenceFile[K: ClassTag, V: ClassTag](path: String, keyClass: Class[K], valueClass: Class[V],
+      cloneKeyValues: Boolean = true): RDD[(K, V)] =
+    sequenceFile(path, keyClass, valueClass, defaultMinSplits, cloneKeyValues)
 
   /**
    * Version of sequenceFile() for types implicitly convertible to Writables through a
@@ -480,8 +490,8 @@ class SparkContext(
    * for the appropriate type. In addition, we pass the converter a ClassTag of its type to
    * allow it to figure out the Writable class to use in the subclass case.
    */
-   def sequenceFile[K, V](path: String, minSplits: Int = defaultMinSplits)
-      (implicit km: ClassTag[K], vm: ClassTag[V],
+   def sequenceFile[K, V](path: String, minSplits: Int = defaultMinSplits,
+       cloneKeyValues: Boolean = true) (implicit km: ClassTag[K], vm: ClassTag[V],
           kcf: () => WritableConverter[K], vcf: () => WritableConverter[V])
       : RDD[(K, V)] = {
     val kc = kcf()
@@ -489,7 +499,7 @@ class SparkContext(
     val format = classOf[SequenceFileInputFormat[Writable, Writable]]
     val writables = hadoopFile(path, format,
         kc.writableClass(km).asInstanceOf[Class[Writable]],
-        vc.writableClass(vm).asInstanceOf[Class[Writable]], minSplits)
+        vc.writableClass(vm).asInstanceOf[Class[Writable]], minSplits, cloneKeyValues)
     writables.map{case (k,v) => (kc.convert(k), vc.convert(v))}
   }
 

core/src/main/scala/org/apache/spark/rdd/HadoopRDD.scala

@@ -19,7 +19,10 @@ package org.apache.spark.rdd
 
 import java.io.EOFException
 
-import org.apache.hadoop.mapred.FileInputFormat
+import scala.reflect.ClassTag
+
+import org.apache.hadoop.conf.{Configuration, Configurable}
+import org.apache.hadoop.io.Writable
 import org.apache.hadoop.mapred.InputFormat
 import org.apache.hadoop.mapred.InputSplit
 import org.apache.hadoop.mapred.JobConf
@@ -31,7 +34,7 @@ import org.apache.spark._
 import org.apache.spark.broadcast.Broadcast
 import org.apache.spark.deploy.SparkHadoopUtil
 import org.apache.spark.util.NextIterator
-import org.apache.hadoop.conf.{Configuration, Configurable}
+import org.apache.spark.util.Utils.cloneWritables
 
 
 /**
@@ -62,14 +65,15 @@ private[spark] class HadoopPartition(rddId: Int, idx: Int, @transient s: InputSp
  * @param valueClass Class of the value associated with the inputFormatClass.
  * @param minSplits Minimum number of Hadoop Splits (HadoopRDD partitions) to generate.
  */
-class HadoopRDD[K, V](
+class HadoopRDD[K: ClassTag, V: ClassTag](
     sc: SparkContext,
     broadcastedConf: Broadcast[SerializableWritable[Configuration]],
     initLocalJobConfFuncOpt: Option[JobConf => Unit],
     inputFormatClass: Class[_ <: InputFormat[K, V]],
     keyClass: Class[K],
     valueClass: Class[V],
-    minSplits: Int)
+    minSplits: Int,
+    cloneKeyValues: Boolean)
   extends RDD[(K, V)](sc, Nil) with Logging {
 
   def this(
@@ -78,7 +82,8 @@ class HadoopRDD[K, V](
       inputFormatClass: Class[_ <: InputFormat[K, V]],
       keyClass: Class[K],
       valueClass: Class[V],
-      minSplits: Int) = {
+      minSplits: Int,
+      cloneKeyValues: Boolean) = {
     this(
       sc,
       sc.broadcast(new SerializableWritable(conf))
@@ -87,7 +92,8 @@ class HadoopRDD[K, V](
       inputFormatClass,
       keyClass,
       valueClass,
-      minSplits)
+      minSplits,
+      cloneKeyValues)
   }
 
   protected val jobConfCacheKey = "rdd_%d_job_conf".format(id)
@@ -158,10 +164,10 @@ class HadoopRDD[K, V](
 
       // Register an on-task-completion callback to close the input stream.
       context.addOnCompleteCallback{ () => closeIfNeeded() }
-
       val key: K = reader.createKey()
+      val keyCloneFunc = cloneWritables[K](getConf)
       val value: V = reader.createValue()
-
+      val valueCloneFunc = cloneWritables[V](getConf)
       override def getNext() = {
         try {
           finished = !reader.next(key, value)
@@ -169,7 +175,12 @@ class HadoopRDD[K, V](
           case eof: EOFException =>
             finished = true
         }
-        (key, value)
+        if (cloneKeyValues) {
+          (keyCloneFunc(key.asInstanceOf[Writable]),
+            valueCloneFunc(value.asInstanceOf[Writable]))
+        } else {
+          (key, value)
+        }
       }
 
       override def close() {

core/src/main/scala/org/apache/spark/rdd/NewHadoopRDD.scala

@@ -20,11 +20,14 @@ package org.apache.spark.rdd
 import java.text.SimpleDateFormat
 import java.util.Date
 
+import scala.reflect.ClassTag
+
 import org.apache.hadoop.conf.{Configurable, Configuration}
 import org.apache.hadoop.io.Writable
 import org.apache.hadoop.mapreduce._
 
 import org.apache.spark.{InterruptibleIterator, Logging, Partition, SerializableWritable, SparkContext, TaskContext}
+import org.apache.spark.util.Utils.cloneWritables
 
 
 private[spark]
@@ -36,12 +39,13 @@ class NewHadoopPartition(rddId: Int, val index: Int, @transient rawSplit: InputS
   override def hashCode(): Int = (41 * (41 + rddId) + index)
 }
 
-class NewHadoopRDD[K, V](
+class NewHadoopRDD[K: ClassTag, V: ClassTag](
     sc : SparkContext,
     inputFormatClass: Class[_ <: InputFormat[K, V]],
     keyClass: Class[K],
     valueClass: Class[V],
-    @transient conf: Configuration)
+    @transient conf: Configuration,
+    cloneKeyValues: Boolean)
   extends RDD[(K, V)](sc, Nil)
   with SparkHadoopMapReduceUtil
   with Logging {
@@ -88,7 +92,8 @@ class NewHadoopRDD[K, V](
 
       // Register an on-task-completion callback to close the input stream.
       context.addOnCompleteCallback(() => close())
-
+      val keyCloneFunc = cloneWritables[K](conf)
+      val valueCloneFunc = cloneWritables[V](conf)
       var havePair = false
       var finished = false
 
@@ -105,7 +110,14 @@ class NewHadoopRDD[K, V](
           throw new java.util.NoSuchElementException("End of stream")
         }
         havePair = false
-        (reader.getCurrentKey, reader.getCurrentValue)
+        val key = reader.getCurrentKey
+        val value = reader.getCurrentValue
+        if (cloneKeyValues) {
+          (keyCloneFunc(key.asInstanceOf[Writable]),
+            valueCloneFunc(value.asInstanceOf[Writable]))
+        } else {
+          (key, value)
+        }
       }
 
       private def close() {

core/src/main/scala/org/apache/spark/util/Utils.scala

@@ -26,23 +26,47 @@ import scala.collection.JavaConversions._
 import scala.collection.Map
 import scala.collection.mutable.ArrayBuffer
 import scala.io.Source
-import scala.reflect.ClassTag
+import scala.reflect.{classTag, ClassTag}
 
 import com.google.common.io.Files
 import com.google.common.util.concurrent.ThreadFactoryBuilder
 
+import org.apache.hadoop.conf.Configuration
 import org.apache.hadoop.fs.{Path, FileSystem, FileUtil}
+import org.apache.hadoop.io._
 
 import org.apache.spark.serializer.{DeserializationStream, SerializationStream, SerializerInstance}
 import org.apache.spark.deploy.SparkHadoopUtil
 import java.nio.ByteBuffer
-import org.apache.spark.{SparkConf, SparkContext, SparkException, Logging}
+import org.apache.spark.{SparkConf, SparkException, Logging}
 
 
 /**
  * Various utility methods used by Spark.
  */
 private[spark] object Utils extends Logging {
+
+  /**
+   *  We try to clone for most common types of writables and we call WritableUtils.clone otherwise
+   *  intention is to optimize, for example for NullWritable there is no need and for Long, int and
+   *  String creating a new object with value set would be faster.
+   */
+  def cloneWritables[T: ClassTag](conf: Configuration): Writable => T = {
+    val cloneFunc = classTag[T] match {
+      case ClassTag(_: Text) => 
+        (w: Writable) => new Text(w.asInstanceOf[Text].getBytes).asInstanceOf[T]
+      case ClassTag(_: LongWritable) => 
+        (w: Writable) => new LongWritable(w.asInstanceOf[LongWritable].get).asInstanceOf[T]
+      case ClassTag(_: IntWritable) => 
+        (w: Writable) => new IntWritable(w.asInstanceOf[IntWritable].get).asInstanceOf[T]
+      case ClassTag(_: NullWritable) => 
+        (w: Writable) => w.asInstanceOf[T] // TODO: should we clone this ?
+      case _ => 
+        (w: Writable) => WritableUtils.clone(w, conf).asInstanceOf[T] // slower way of cloning.
+    }
+    cloneFunc
+  }
+
   /** Serialize an object using Java serialization */
   def serialize[T](o: T): Array[Byte] = {
     val bos = new ByteArrayOutputStream()