Question

我正在尝试将流数据保存到卡夫卡的cassandra中。我能够读取和解析数据但是当我在下面的行中调用以保存数据时，我得到Task not Serializable异常。我的课程正在扩展可序列化，但不确定为什么我看到这个错误，谷歌搜索3小时后没有得到太多的帮助，有些机构可以提供任何指示吗？

val collection = sc.parallelize(Seq((obj.id, obj.data)))
collection.saveToCassandra("testKS", "testTable ", SomeColumns("id", "data"))` 


import org.apache.spark.SparkConf
import org.apache.spark.SparkContext
import org.apache.spark.sql.SaveMode
import org.apache.spark.streaming.Seconds
import org.apache.spark.streaming.StreamingContext
import org.apache.spark.streaming.kafka.KafkaUtils
import com.datastax.spark.connector._

import kafka.serializer.StringDecoder
import org.apache.spark.rdd.RDD
import com.datastax.spark.connector.SomeColumns
import java.util.Formatter.DateTime

object StreamProcessor extends Serializable {
  def main(args: Array[String]): Unit = {
    val sparkConf = new SparkConf().setMaster("local[2]").setAppName("StreamProcessor")
      .set("spark.cassandra.connection.host", "127.0.0.1")

    val sc = new SparkContext(sparkConf)

    val ssc = new StreamingContext(sc, Seconds(2))

    val sqlContext = new SQLContext(sc)

    val kafkaParams = Map("metadata.broker.list" -> "localhost:9092")

    val topics = args.toSet

    val stream = KafkaUtils.createDirectStream[String, String, StringDecoder, StringDecoder](
      ssc, kafkaParams, topics)

    stream.foreachRDD { rdd =>

      if (!rdd.isEmpty()) {
        try {

          rdd.foreachPartition { iter =>
            iter.foreach {
              case (key, msg) =>

                val obj = msgParseMaster(msg)

                val collection = sc.parallelize(Seq((obj.id, obj.data)))
                collection.saveToCassandra("testKS", "testTable ", SomeColumns("id", "data"))

            }
          }

        }

      }
    }

    ssc.start()
    ssc.awaitTermination()

  }

  import org.json4s._
  import org.json4s.native.JsonMethods._
  case class wordCount(id: Long, data: String) extends serializable
  implicit val formats = DefaultFormats
  def msgParseMaster(msg: String): wordCount = {
    val m = parse(msg).extract[wordCount]
    return m

  }

}

我正在

org.apache.spark.SparkException：任务不可序列化

以下是完整日志

16/08/06 10:24:52错误JobScheduler：运行作业流作业时出错1470504292000 ms.0 org.apache.spark.SparkException：任务不可序列化在org.apache.spark.util.ClosureCleaner $ .ensureSerializable（ClosureCleaner.scala：304）在org.apache.spark.util.ClosureCleaner $ .org $ apache $ spark $ util $ ClosureCleaner $$ clean（ClosureCleaner.scala：294）在org.apache.spark.util.ClosureCleaner $ .clean（ClosureCleaner.scala：122）在org.apache.spark.SparkContext.clean（SparkContext.scala：2055）在org.apache.spark.rdd.RDD $$ anonfun $ foreachPartition $ 1.apply（RDD.scala：919）在org.apache.spark.rdd.RDD $$ anonfun $ foreachPartition $ 1.apply（RDD.scala：918）在org.apache.spark.rdd.RDDOperationScope $ .withScope（RDDOperationScope.scala：150）在org.apache.spark.rdd.RDDOperationScope $ .withScope（RDDOperationScope.scala：111）在org.apache.spark.rdd.RDD.withScope（RDD.scala：316）在org.apache.spark.rdd.RDD.foreachPartition（RDD.scala：918）在

Answer 1

SparkContext不可序列化，您无法在foreachRDD内使用它，并且使用图表时您不需要它。相反，您可以简单地映射每个RDD，解析相关数据并将新RDD保存到cassandra：

stream
  .map { 
    case (_, msg) => 
      val result = msgParseMaster(msg)
      (result.id, result.data)
   }
  .foreachRDD(rdd => if (!rdd.isEmpty)
                       rdd.saveToCassandra("testKS",
                                           "testTable",
                                            SomeColumns("id", "data")))

Answer 2

你不能在传递给sc.parallelize的函数中调用foreachPartition - 该函数必须被序列化并发送给每个执行者，并且SparkContext（有意）不可序列化（它应该只存在于驱动程序应用程序中，而不是执行程序中。

无法在foreachRDD中序列化SparkContext

2 个答案: