title: Apache Spark Throws java.lang.IllegalStateException: unread block data
body: <p>What we are doing is:</p>
  
  <ol>
  <li>Installing Spark 0.9.1 according to the documentation on the website, along with CDH4 (and another cluster with CDH5) distros of hadoop/hdfs.</li>
  <li>Building a fat jar with a Spark app with sbt then trying to run it on the cluster</li>
  </ol>
  
  <p>I've also included code snippets, and sbt deps at the bottom.</p>
  
  <p>When I've Googled this, there seems to be two somewhat vague responses:
  a) Mismatching spark versions on nodes/user code
  b) Need to add more jars to the SparkConf</p>
  
  <p>Now I know that (b) is not the problem having successfully run the same code on other clusters while only including one jar (it's a fat jar).</p>
  
  <p>But I have no idea how to check for (a) - it appears Spark doesn't have any version checks or anything - it would be nice if it checked versions and threw a "mismatching version exception: you have user code using version X and node Y has version Z".</p>
  
  <p>I would be very grateful for advice on this.  I've submitted a bug report, because there has to be something wrong with the Spark documentation because I've seen two independent sysadms get the exact same problem with different versions of CDH on different clusters. <a href="https://issues.apache.org/jira/browse/SPARK-1867">https://issues.apache.org/jira/browse/SPARK-1867</a></p>
  
  <p>The exception:</p>
  
  <pre><code>Exception in thread "main" org.apache.spark.SparkException: Job aborted: Task 0.0:1 failed 32 times (most recent failure: Exception failure: java.lang.IllegalStateException: unread block data)
      at org.apache.spark.scheduler.DAGScheduler$$anonfun$org$apache$spark$scheduler$DAGScheduler$$abortStage$1.apply(DAGScheduler.scala:1020)
      at org.apache.spark.scheduler.DAGScheduler$$anonfun$org$apache$spark$scheduler$DAGScheduler$$abortStage$1.apply(DAGScheduler.scala:1018)
      at scala.collection.mutable.ResizableArray$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$$abortStage(DAGScheduler.scala:1018)
      at org.apache.spark.scheduler.DAGScheduler$$anonfun$processEvent$10.apply(DAGScheduler.scala:604)
      at org.apache.spark.scheduler.DAGScheduler$$anonfun$processEvent$10.apply(DAGScheduler.scala:604)
      at scala.Option.foreach(Option.scala:236)
      at org.apache.spark.scheduler.DAGScheduler.processEvent(DAGScheduler.scala:604)
      at org.apache.spark.scheduler.DAGScheduler$$anonfun$start$1$$anon$2$$anonfun$receive$1.applyOrElse(DAGScheduler.scala:190)
      at akka.actor.ActorCell.receiveMessage(ActorCell.scala:498)
      at akka.actor.ActorCell.invoke(ActorCell.scala:456)
      at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:237)
      at akka.dispatch.Mailbox.run(Mailbox.scala:219)
      at akka.dispatch.ForkJoinExecutorConfigurator$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)
  14/05/16 18:05:31 INFO scheduler.TaskSetManager: Loss was due to java.lang.IllegalStateException: unread block data [duplicate 59]
  </code></pre>
  
  <p>My code snippet:</p>
  
  <pre><code>val conf = new SparkConf()
                 .setMaster(clusterMaster)
                 .setAppName(appName)
                 .setSparkHome(sparkHome)
                 .setJars(SparkContext.jarOfClass(this.getClass))
  
  println("count = " + new SparkContext(conf).textFile(someHdfsPath).count())
  </code></pre>
  
  <p>My SBT dependencies:</p>
  
  <pre><code>// relevant
  "org.apache.spark" % "spark-core_2.10" % "0.9.1",
  "org.apache.hadoop" % "hadoop-client" % "2.3.0-mr1-cdh5.0.0",
  
  // standard, probably unrelated
  "com.github.seratch" %% "awscala" % "[0.2,)",
  "org.scalacheck" %% "scalacheck" % "1.10.1" % "test",
  "org.specs2" %% "specs2" % "1.14" % "test",
  "org.scala-lang" % "scala-reflect" % "2.10.3",
  "org.scalaz" %% "scalaz-core" % "7.0.5",
  "net.minidev" % "json-smart" % "1.2"
  </code></pre>