apache-spark - 为什么 Spark on YARN 在集群模式下失败并显示 "Exception in thread "驱动程序“java.lang.NullPointerException”？

Question

我将 emr-5.4.0 与 Spark 2.1.0 一起使用。我懂什么NullPointerException是，这个问题是关于为什么在这种特殊情况下抛出的。

无法真正弄清楚为什么我在驱动程序线程中得到 NullPointerException。

我的这个奇怪的工作因这个错误而失败:

18/03/29 20:07:52 INFO ApplicationMaster: Starting the user application in a separate Thread
18/03/29 20:07:52 INFO ApplicationMaster: Waiting for spark context initialization...
Exception in thread "Driver" java.lang.NullPointerException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.spark.deploy.yarn.ApplicationMaster$$anon$2.run(ApplicationMaster.scala:637)
18/03/29 20:07:52 ERROR ApplicationMaster: Uncaught exception:
java.lang.IllegalStateException: SparkContext is null but app is still running!
    at org.apache.spark.deploy.yarn.ApplicationMaster.runDriver(ApplicationMaster.scala:415)
    at org.apache.spark.deploy.yarn.ApplicationMaster.run(ApplicationMaster.scala:254)
    at org.apache.spark.deploy.yarn.ApplicationMaster$$anonfun$main$1.apply$mcV$sp(ApplicationMaster.scala:766)
    at org.apache.spark.deploy.SparkHadoopUtil$$anon$1.run(SparkHadoopUtil.scala:67)
    at org.apache.spark.deploy.SparkHadoopUtil$$anon$1.run(SparkHadoopUtil.scala:66)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:422)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1698)
    at org.apache.spark.deploy.SparkHadoopUtil.runAsSparkUser(SparkHadoopUtil.scala:66)
    at org.apache.spark.deploy.yarn.ApplicationMaster$.main(ApplicationMaster.scala:764)
    at org.apache.spark.deploy.yarn.ApplicationMaster.main(ApplicationMaster.scala)
18/03/29 20:07:52 INFO ApplicationMaster: Final app status: FAILED, exitCode: 10, (reason: Uncaught exception: java.lang.IllegalStateException: SparkContext is null but app is still running!)
18/03/29 20:07:52 INFO ApplicationMaster: Unregistering ApplicationMaster with FAILED (diag message: Uncaught exception: java.lang.IllegalStateException: SparkContext is null but app is still running!)
18/03/29 20:07:52 INFO ApplicationMaster: Deleting staging directory hdfs://<ip-address>.ec2.internal:8020/user/hadoop/.sparkStaging/application_1522348295743_0010
18/03/29 20:07:52 INFO ShutdownHookManager: Shutdown hook called
End of LogType:stderr

我提交了这份工作:

spark-submit --deploy-mode cluster --master yarn --num-executors 40 --executor-cores 16 --executor-memory 100g --driver-cores 8 --driver-memory 100g --class <package.class_name> --jars <s3://s3_path/some_lib.jar> <s3://s3_path/class.jar>

我的类(class)看起来像这样:

class MyClass {

  def main(args: Array[String]): Unit = {
    val c = new MyClass()
    c.process()
  }

  def process(): Unit = {
    val sparkConf = new SparkConf().setAppName("my-test")
    val sparkSession: SparkSession = SparkSession.builder().config(sparkConf).getOrCreate()
    import sparkSession.implicits._
    ....
  }

  ...
}

Answer 1

更改 class MyClass至 object MyClass你就完成了。

当我们在做的时候，我也会改变 class MyClass至 object MyClass extends App并删除 def main(args: Array[String]): Unit (由 extends App 给出)。

我报告了 Spark 2.3.0 的改进 - [SPARK-23830] Spark on YARN in cluster deploy mode fail with NullPointerException when a Spark application is a Scala class not object - 将它很好地报告给最终用户。

深入了解 Spark on YARN 的工作原理，以下消息是 ApplicationMaster of a Spark application starts the driver (您使用 --deploy-mode cluster --master yarn 和 spark-submit )。

ApplicationMaster: Starting the user application in a separate Thread

在 INFO 消息之后，您应该会看到另一个:

ApplicationMaster: Waiting for spark context initialization...

这是 driver initialization when the ApplicationMaster runs 的一部分.

异常原因 Exception in thread "Driver" java.lang.NullPointerException是由于 following code :

val mainMethod = userClassLoader.loadClass(args.userClass)
  .getMethod("main", classOf[Array[String]])

我的理解是 mainMethod是 null至此 following line (其中 mainMethod 是 null )“触发器” NullPointerException :

mainMethod.invoke(null, userArgs.toArray)

该线程确实被称为 Driver (如在 Exception in thread "Driver" java.lang.NullPointerException 中)如在 this line 中设置:

userThread.setContextClassLoader(userClassLoader)
userThread.setName("Driver")
userThread.start()

行号不同，因为我使用 Spark 2.3.0 来引用行，而您将 emr-5.4.0 与 Spark 2.1.0 一起使用。