Github user mateiz commented on a diff in the pull request:
https://github.com/apache/spark/pull/1520#discussion_r15215432
--- Diff: mllib/src/main/scala/org/apache/spark/mllib/rdd/RandomRDD.scala
---
@@ -0,0 +1,140 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.mllib.rdd
+
+import org.apache.spark.{Partition, SparkContext, TaskContext}
+import org.apache.spark.mllib.linalg.{DenseVector, Vector}
+import org.apache.spark.mllib.random.DistributionGenerator
+import org.apache.spark.rdd.RDD
+import org.apache.spark.util.Utils
+
+private[mllib] class RandomRDDPartition(val idx: Int,
+ val size: Long,
+ val rng: DistributionGenerator,
+ val seed: Long) extends Partition {
+
+ override val index: Int = idx
+
+}
+
+// These two classes are necessary since Range objects in Scala cannot
have size > Int.MaxValue
+private[mllib] class RandomRDD(@transient private var sc: SparkContext,
+ size: Long,
+ numSlices: Int,
+ @transient rng: DistributionGenerator,
+ @transient seed: Long = Utils.random.nextLong) extends RDD[Double](sc,
Nil) {
+
+ require(size > 0, "Positive RDD size required.")
+ require(numSlices > 0, "Positive number of partitions required")
+
+ override def compute(splitIn: Partition, context: TaskContext):
Iterator[Double] = {
+ val split = splitIn.asInstanceOf[RandomRDDPartition]
+ RandomRDD.getPointIterator(split)
+ }
+
+ override def getPartitions: Array[Partition] = {
+ RandomRDD.getPartitions(size, numSlices, rng, seed)
+ }
+}
+
+private[mllib] class RandomVectorRDD(@transient private var sc:
SparkContext,
+ size: Long,
+ vectorSize: Int,
+ numSlices: Int,
+ @transient rng: DistributionGenerator,
+ @transient seed: Long = Utils.random.nextLong) extends RDD[Vector](sc,
Nil) {
+
+ require(size > 0, "Positive RDD size required.")
+ require(numSlices > 0, "Positive number of partitions required")
+ require(vectorSize > 0, "Positive vector size required.")
+
+ override def compute(splitIn: Partition, context: TaskContext):
Iterator[Vector] = {
+ val split = splitIn.asInstanceOf[RandomRDDPartition]
+ RandomRDD.getVectorIterator(split, vectorSize)
+ }
+
+ override protected def getPartitions: Array[Partition] = {
+ RandomRDD.getPartitions(size, numSlices, rng, seed)
+ }
+}
+
+private[mllib] object RandomRDD {
+
+ private[mllib] class FixedSizePointIterator(val numElem: Long, val rng:
DistributionGenerator)
+ extends Iterator[Double] {
+
+ private var currentSize = 0
+
+ override def hasNext: Boolean = currentSize < numElem
+
+ override def next(): Double = {
+ currentSize += 1
+ rng.nextValue()
+ }
+ }
+
+ private[mllib] class FixedSizeVectorIterator(val numElem: Long,
+ val vectorSize: Int,
+ val rng: DistributionGenerator)
+ extends Iterator[Vector] {
+
+ private var currentSize = 0
+
+ override def hasNext: Boolean = currentSize < numElem
+
+ override def next(): Vector = {
+ currentSize += 1
+ new DenseVector((0 until vectorSize).map { _ => rng.nextValue()
}.toArray)
+ }
+ }
+
+ def getPartitions(size: Long,
+ numSlices: Int,
+ rng: DistributionGenerator,
+ seed: Long): Array[Partition] = {
+
+ val firstPartitionSize = size / numSlices + size % numSlices
+ val otherPartitionSize = size / numSlices
+
+ val partitions = new Array[RandomRDDPartition](numSlices)
+ var i = 0
+ while (i < numSlices) {
+ partitions(i) = if (i == 0) {
+ new RandomRDDPartition(i, firstPartitionSize, rng, seed)
+ } else {
+ new RandomRDDPartition(i, otherPartitionSize, rng.newInstance(),
seed)
+ }
+ i += 1
+ }
+ partitions.asInstanceOf[Array[Partition]]
+ }
+
+ // The RNG has to be reset every time the iterator is requested to
guarantee same data
+ // every time the content of the RDD is examined.
+ def getPointIterator(partition: RandomRDDPartition): Iterator[Double] = {
+ partition.rng.setSeed(partition.seed + partition.index)
--- End diff --
Instead of doing this, it would be better to give each partition a seed
generated by a Random object based on the RDD's seed. This way the seeds differ
in more bits from each other. For example, take a look at
PartitionwiseSampledRDD in the current codebase. It uses an RDD-wide seed to
create a sequence of seeds, once for each partition, then it takes those as
input to new RNGs for each partition.
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