来自 RDD 映射的 Spark Scala 序列化错误

Question

我有一个格式为 RDD[((Long, Long), (Long, Long))] 的 RDD，我需要转换或转换为 RDD[((Long, Long), (Long, Long, Long, Long ))] 其中第二个 RDD 元组基于第一个 RDD 中的函数。

我正在尝试实现这个基于地图的功能，但是我认为这里做错了。请帮我解决问题。

这里是完整的代码：

package com.ranker.correlation.listitem
import org.apache.spark.SparkConf
import org.apache.spark.SparkContext
import org.apache.spark.SparkContext._
import org.apache.spark.rdd._
import scala.collection.Map

class ListItemCorrelation(sc: SparkContext) extends Serializable {

  def up_down(dirX: Long, dirY: Long): (Long, Long, Long, Long) = {
    if (dirX.equals(1)) {
      if (dirY.equals(1)) {
        return (1, 0, 0, 0)
      } else {
        return (0, 1, 0, 0)
      }
    } else {
      if (dirY.equals(1)) {
        return (0, 0, 1, 0)
      } else {
        return (0, 0, 0, 1)
      }
    }
  }

  def run(votes: String):  RDD[((Long, Long), (Long, Long, Long, Long))]   = {
    val userVotes = sc.textFile(votes)
    val userVotesPairs = userVotes.map { t =>
      val p = t.split(",")
      (p(0).toLong, (p(1).toLong, p(2).toLong))
    }
    val jn = userVotesPairs.join(userVotesPairs).values.filter(t => t._1._1.<(t._2._1))
    val first = jn.map(t => ((t._1._1, t._2._1), (t._1._2, t._2._2)))
    var second = first.map(t => ((t._1._1, t._2._1), up_down(t._1._2, t._2._2)))
    //More functionality
    return result
  }

}
object ListItemCorrelation extends Serializable {
  def main(args: Array[String]) {
    val votes = args(0)
    val conf = new SparkConf().setAppName("SparkJoins").setMaster("local")
    val context = new SparkContext(conf)
    val job = new ListItemCorrelation(context)
    val results = job.run(votes)
    val output = args(1)
    results.saveAsTextFile(output)
    context.stop()
  }
}

当我尝试运行此脚本时，出现以下错误：

线程“主”org.apache.spark.SparkException 中的异常：任务不是 可序列化在 org.apache.spark.util.ClosureCleaner$.ensureSerializable(ClosureCleaner.scala:298) 在 org.apache.spark.util.ClosureCleaner$.org$apache$spark$util$ClosureCleaner$$clean(ClosureCleaner.scala:288) 在 org.apache.spark.util.ClosureCleaner$.clean(ClosureCleaner.scala:108) 在 org.apache.spark.SparkContext.clean(SparkContext.scala:2094) 在 org.apache.spark.rdd.RDD$$anonfun$map$1.apply(RDD.scala:370) 在 org.apache.spark.rdd.RDD$$anonfun$map$1.apply(RDD.scala:369) 在 org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:151) 在 org.apache.spark.rdd.RDDOperationScope$.withScope(RDDOperationScope.scala:112) 在 org.apache.spark.rdd.RDD.withScope(RDD.scala:362) 在 org.apache.spark.rdd.RDD.map(RDD.scala:369) 在 com.ranker.correlation.listitem.ListItemCorrelation.run(ListItemCorrelation.scala:34) 在 com.ranker.correlation.listitem.ListItemCorrelation$.main(ListItemCorrelation.scala:47) 在 com.ranker.correlation.listitem.ListItemCorrelation.main(ListItemCorrelation.scala) 引起：java.io.NotSerializableException： org.apache.spark.SparkContext 序列化栈： - 对象不可序列化（类：org.apache.spark.SparkContext，值：org.apache.spark.SparkContext@4248e66b） - 字段（类：com.ranker.correlation.listitem.ListItemCorrelation，名称：sc，类型：类 org.apache.spark.SparkContext） - 对象（com.ranker.correlation.listitem.ListItemCorrelation 类，com.ranker.correlation.listitem.ListItemCorrelation@270b6b5e） - 字段（类：com.ranker.correlation.listitem.ListItemCorrelation$$anonfun$4，名称： $外部，类型：类 com.ranker.correlation.listitem.ListItemCorrelation) - 对象（com.ranker.correlation.listitem.ListItemCorrelation$$anonfun$4 类， ） 在 org.apache.spark.serializer.SerializationDebugger$.improveException(SerializationDebugger.scala:40) 在 org.apache.spark.serializer.JavaSerializationStream.writeObject(JavaSerializer.scala:46) 在 org.apache.spark.serializer.JavaSerializerInstance.serialize(JavaSerializer.scala:100) 在 org.apache.spark.util.ClosureCleaner$.ensureSerializable(ClosureCleaner.scala:295) ... 12 更多

执行以下行时发生此错误：

var second = first.map(t => ((t._1._1, t._2._1), up_down(t._1._2, t._2._2)))

我对 scala 很陌生，请帮助我找到正确的方法。

Answer 1

将up_down 方法放在伴随对象上。当在 RDD 闭包中访问任何类变量时，该类（以及其中的所有内容，如 SparkContext）都会被序列化。方法参数在这里算作类变量。使用静态对象可以解决这个问题：

package com.ranker.correlation.listitem
import org.apache.spark.SparkConf
import org.apache.spark.SparkContext
import org.apache.spark.SparkContext._
import org.apache.spark.rdd._
import scala.collection.Map

object ListItemCorrelation {
  def up_down(dirX: Long, dirY: Long): (Long, Long, Long, Long) = {
    if (dirX.equals(1)) {
      if (dirY.equals(1)) {
        return (1, 0, 0, 0)
      } else {
        return (0, 1, 0, 0)
      }
    } else {
      if (dirY.equals(1)) {
        return (0, 0, 1, 0)
      } else {
        return (0, 0, 0, 1)
      }
    }
  }
}


class ListItemCorrelation(sc: SparkContext) extends Serializable {

  def run(votes: String):  RDD[((Long, Long), (Long, Long, Long, Long))]   = {
    val userVotes = sc.textFile(votes)
    val userVotesPairs = userVotes.map { t =>
      val p = t.split(",")
      (p(0).toLong, (p(1).toLong, p(2).toLong))
    }
    val jn = userVotesPairs.join(userVotesPairs).values.filter(t => t._1._1.<(t._2._1))
    val first = jn.map(t => ((t._1._1, t._2._1), (t._1._2, t._2._2)))
    var second = first.map(t => ((t._1._1, t._2._1), ListItemCorrelation.up_down(t._1._2, t._2._2)))
    //More functionality
    return result
  }

}
object ListItemCorrelation extends Serializable {
  def main(args: Array[String]) {
    val votes = args(0)
    val conf = new SparkConf().setAppName("SparkJoins").setMaster("local")
    val context = new SparkContext(conf)
    val job = new ListItemCorrelation(context)
    val results = job.run(votes)
    val output = args(1)
    results.saveAsTextFile(output)
    context.stop()
  }
}