使用元组

Question

我使用GraphX API for spark来构建图表并使用Pregel API处理它。如果我从vprog函数返回一个参数元组，则不会发生错误，但如果我使用相同的元组返回一个新元组，则会得到零点错误。 以下是相关代码：

val verticesRDD = cleanDtaDF.select("ChildHash", "DN").rdd.map(row => (row(0).toString.toLong, (row(1).toString.toDouble,row(0).toString.toLong)))

val edgesRDD = (rawDtaDF.select("ChildHash", "ParentHash", "dealer_code", "dealer_customer_number", "parent_dealer_cust_number").rdd
        .map(row => Edge(row.get(0).toString.toLong, row.get(1).toString.toLong, (row(3) + " is a child of " + row(4), " when dealer is " + row.get(2)))))

val myGraph = Graph(verticesRDD, edgesRDD)

def vprog(vertexId: VertexId, vertexDTA:(Double, Long), msg: Double): (Double, Long) = {
        (vertexDTA._1, vertexDTA._2)
}
val result = myGraph.pregel(0.0, 1, activeDirection = EdgeDirection.Out)(vprog,t => Iterator((t.dstId, t.srcAttr._2)),(x, y) => x + y)

如果我对vprog（...）进行简单的更改，则不会发生错误 - 不能访问元组＆＃39;成员：

def vprog(vertexId: VertexId, vertexDTA:(Double, Long), msg: Double): (Double, Long) = {
        vertexDTA
}

错误是

[Stage 101:>              (0 + 0) / 200][Stage 102:>              (0 + 4) / 200]18/03/10 20:43:16 WARN scheduler.TaskSetManager: Lost task 1.0 in stage 102.0 (TID 5959, ue1lslaved25.na.aws.cat.com, executor 146): java.lang.NullPointerException
        at $line69.$read$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw.vprog(<console>:60)
        at $line70.$read$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$anonfun$2.apply(<console>:75)
        at $line70.$read$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$anonfun$2.apply(<console>:75)
        at org.apache.spark.graphx.Pregel$$anonfun$1.apply(Pregel.scala:125)
        at org.apache.spark.graphx.Pregel$$anonfun$1.apply(Pregel.scala:125)
        at org.apache.spark.graphx.impl.VertexPartitionBaseOps.map(VertexPartitionBaseOps.scala:61)
        at org.apache.spark.graphx.impl.GraphImpl$$anonfun$5.apply(GraphImpl.scala:129)
        at org.apache.spark.graphx.impl.GraphImpl$$anonfun$5.apply(GraphImpl.scala:129)
        at scala.collection.Iterator$$anon$11.next(Iterator.scala:409)
        at org.apache.spark.storage.memory.MemoryStore.putIteratorAsValues(MemoryStore.scala:216)
        at org.apache.spark.storage.BlockManager$$anonfun$doPutIterator$1.apply(BlockManager.scala:988)
        at org.apache.spark.storage.BlockManager$$anonfun$doPutIterator$1.apply(BlockManager.scala:979)
        at org.apache.spark.storage.BlockManager.doPut(BlockManager.scala:919)
        at org.apache.spark.storage.BlockManager.doPutIterator(BlockManager.scala:979)
        at org.apache.spark.storage.BlockManager.getOrElseUpdate(BlockManager.scala:697)
        at org.apache.spark.rdd.RDD.getOrCompute(RDD.scala:334)
        at org.apache.spark.rdd.RDD.iterator(RDD.scala:285)
        at org.apache.spark.rdd.MapPartitionsRDD.compute(MapPartitionsRDD.scala:38)
        at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:323)
        at org.apache.spark.rdd.RDD.iterator(RDD.scala:287)
        at org.apache.spark.scheduler.ShuffleMapTask.runTask(ShuffleMapTask.scala:96)
        at org.apache.spark.scheduler.ShuffleMapTask.runTask(ShuffleMapTask.scala:53)
        at org.apache.spark.scheduler.Task.run(Task.scala:99)
        at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:322)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:745)

Answer 1

这个问题有一个简单的解释。它与Spark或Graphx无关。

拥有该功能（只是从原件中删除不相关的项目）：

def vprog(vertexDTA:(Double, Long)): (Double, Long) = {
   (vertexDTA._1, vertexDTA._2)
}

如果arg vertexDTA为null，则vertexDTA._1和vertexDTA._2都会抛出NullPointerException。

如果我们将功能更改为

def vprog(vertexDTA:(Double, Long)): (Double, Long) = {
   vertexDTA
}

当arg为null时，它只是返回它，无法访问元组的成员，因此没有NPE。