[SPARK-1012] DAGScheduler Exception

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.9.0
• Fix Version/s: 0.9.0
• Component/s: Spark Core
• Labels: DAGScheduler MLLib,
• Assignee: Hossein Falaki
• Reporter: Hossein Falaki
• Created: 02/Jan/14 16:19
• Updated: 07/Jan/14 22:02
• Resolved: 07/Jan/14 22:02

Description

I get
When running the following code:

import org.apache.spark.mllib.recommendation.ALS
import org.apache.spark.mllib.recommendation.Rating

// Load and parse the data
val data = sc.textFile("mllib/data/als/test.data")
val ratings = data.map(_.split(',') match {
    case Array(user, item, rate) =>  Rating(user.toInt, item.toInt, rate.toDouble)
})

// Build the recommendation model using ALS
val numIterations = 20
val model = ALS.train(ratings, 1, 20, 0.01)

// Evaluate the model on rating data
val ratesAndPreds = ratings.map{ case Rating(user, item, rate) => (rate, model.predict(user, item))}
val MSE = ratesAndPreds.map{ case(v, p) => math.pow((v - p), 2)}.reduce(_ + _)/ratesAndPreds.count

I get:

org.apache.spark.SparkException: Job aborted: Task 2.0:0 failed 1 times (most recent failure: Exception failure: scala.MatchError: null)
	at org.apache.spark.scheduler.DAGScheduler$$anonfun$org$apache$spark$scheduler$DAGScheduler$$abortStage$1.apply(DAGScheduler.scala:1026)
	at org.apache.spark.scheduler.DAGScheduler$$anonfun$org$apache$spark$scheduler$DAGScheduler$$abortStage$1.apply(DAGScheduler.scala:1024)
	at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
	at org.apache.spark.scheduler.DAGScheduler.org$apache$spark$scheduler$DAGScheduler$$abortStage(DAGScheduler.scala:1024)
	at org.apache.spark.scheduler.DAGScheduler$$anonfun$processEvent$10.apply(DAGScheduler.scala:617)
	at org.apache.spark.scheduler.DAGScheduler$$anonfun$processEvent$10.apply(DAGScheduler.scala:617)
	at scala.Option.foreach(Option.scala:236)
	at org.apache.spark.scheduler.DAGScheduler.processEvent(DAGScheduler.scala:617)
	at org.apache.spark.scheduler.DAGScheduler$$anonfun$start$1$$anon$2$$anonfun$receive$1.applyOrElse(DAGScheduler.scala:205)
	at akka.actor.ActorCell.receiveMessage(ActorCell.scala:498)
	at akka.actor.ActorCell.invoke(ActorCell.scala:456)
	at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:237)
	at akka.dispatch.Mailbox.run(Mailbox.scala:219)
	at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:386)
	at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
	at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
	at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
	at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)

The problem is deterministic. In addition ratesAndPreds has exactly 16 elements:

scala> ratesAndPreds.take(16)
res1: Array[(Double, Double)] = Array((5.0,2.9995813468435633), (1.0,2.999581386744982), (5.0,2.9995813468435633), (1.0,2.999581386744982), (5.0,2.9995813468435633), (1.0,2.999581386744982), (5.0,2.9995813468435633), (1.0,2.999581386744982), (1.0,2.999581373444509), (5.0,2.999581413345928), (1.0,2.999581373444509), (5.0,2.999581413345928), (1.0,2.999581373444509), (5.0,2.999581413345928), (1.0,2.999581373444509), (5.0,2.999581413345928))

scala> ratesAndPreds.count()

Throws the exception again.