任务在 spark 中有一个不可序列化的结果

Question

我正在尝试使用 cassandra 驱动程序读取 cassandra table。这是代码。

val x = 1 to 2
val rdd = sc.parallelize(x)

val query = "Select data from testkeyspace.testtable where id=%d"

val cc = CassandraConnector(sc.getConf)

val res1 =
    rdd.map{ it => 
            cc.withSessionDo{ session =>
            session.execute( query.format(it))
        }
     }

res1.take(1).foreach(println)

但我收到异常 Task had a not serializable result。

  org.apache.spark.SparkException: Job aborted due to stage failure: Task 1.0 in stage 24.0 (TID 77) had a not serializable result: com.datastax.driver.core.ArrayBackedResultSet$SinglePage
    at org.apache.spark.scheduler.DAGScheduler.org$apache$spark$scheduler$DAGScheduler$$failJobAndIndependentStages(DAGScheduler.scala:1185)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage.apply(DAGScheduler.scala:1174)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage.apply(DAGScheduler.scala:1173)
    at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
    at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
    at org.apache.spark.scheduler.DAGScheduler.abortStage(DAGScheduler.scala:1173)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed.apply(DAGScheduler.scala:688)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed.apply(DAGScheduler.scala:688)
    at scala.Option.foreach(Option.scala:236)
    at org.apache.spark.scheduler.DAGScheduler.handleTaskSetFailed(DAGScheduler.scala:688)
    at org.apache.spark.scheduler.DAGSchedulerEventProcessActor$$anonfun$receive.applyOrElse(DAGScheduler.scala:1391)
    at akka.actor.ActorCell.receiveMessage(ActorCell.scala:498)
    at akka.actor.ActorCell.invoke(ActorCell.scala:456)
    at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:237)
    at akka.dispatch.Mailbox.run(Mailbox.scala:219)
    at akka.dispatch.ForkJoinExecutorConfigurator$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)

如何解决这个问题？

Answer 1

我们转换中的不可序列化对象是从 Cassandra 返回的结果，它是查询结果的可迭代对象。您通常希望将该集合具体化到 RDD 中。

一种方法是询问该查询产生的所有记录：

session.execute( query.format(it)).all()

任务在 spark 中有一个不可序列化的结果

Task had a not serializable result in spark

apache-spark

spark-cassandra-connector