使用Apache Spark将RDD写为文本文件

Question

我正在探索Spark进行批处理。我正在使用独立模式在本地计算机上运行spark。

我正在尝试使用saveTextFile（）方法将Spark RDD转换为单个文件[最终输出]，但无法正常工作。

例如，如果我有多个分区，我们如何获得一个文件作为最终输出。

更新：

我尝试了以下方法，但是我得到了空指针异常。

person.coalesce(1).toJavaRDD().saveAsTextFile("C://Java_All//output");
person.repartition(1).toJavaRDD().saveAsTextFile("C://Java_All//output");

例外是：

    15/06/23 18:25:27 INFO Executor: Running task 0.0 in stage 1.0 (TID 1)
15/06/23 18:25:27 INFO deprecation: mapred.output.dir is deprecated. Instead, use mapreduce.output.fileoutputformat.outputdir
15/06/23 18:25:27 INFO deprecation: mapred.output.key.class is deprecated. Instead, use mapreduce.job.output.key.class
15/06/23 18:25:27 INFO deprecation: mapred.output.value.class is deprecated. Instead, use mapreduce.job.output.value.class
15/06/23 18:25:27 INFO deprecation: mapred.working.dir is deprecated. Instead, use mapreduce.job.working.dir
15/06/23 18:25:27 ERROR Executor: Exception in task 0.0 in stage 1.0 (TID 1)
java.lang.NullPointerException
    at java.lang.ProcessBuilder.start(ProcessBuilder.java:1012)
    at org.apache.hadoop.util.Shell.runCommand(Shell.java:404)
    at org.apache.hadoop.util.Shell.run(Shell.java:379)
    at org.apache.hadoop.util.Shell$ShellCommandExecutor.execute(Shell.java:589)
    at org.apache.hadoop.util.Shell.execCommand(Shell.java:678)
    at org.apache.hadoop.util.Shell.execCommand(Shell.java:661)
    at org.apache.hadoop.fs.RawLocalFileSystem.setPermission(RawLocalFileSystem.java:639)
    at org.apache.hadoop.fs.FilterFileSystem.setPermission(FilterFileSystem.java:468)
    at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:456)
    at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:424)
    at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:905)
    at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:798)
    at org.apache.hadoop.mapred.TextOutputFormat.getRecordWriter(TextOutputFormat.java:123)
    at org.apache.spark.SparkHadoopWriter.open(SparkHadoopWriter.scala:90)
    at org.apache.spark.rdd.PairRDDFunctions$$anonfun$saveAsHadoopDataset$1$$anonfun$13.apply(PairRDDFunctions.scala:1104)
    at org.apache.spark.rdd.PairRDDFunctions$$anonfun$saveAsHadoopDataset$1$$anonfun$13.apply(PairRDDFunctions.scala:1095)
    at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:63)
    at org.apache.spark.scheduler.Task.run(Task.scala:70)
    at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:213)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
15/06/23 18:25:27 WARN TaskSetManager: Lost task 0.0 in stage 1.0 (TID 1, localhost): java.lang.NullPointerException
    at java.lang.ProcessBuilder.start(ProcessBuilder.java:1012)
    at org.apache.hadoop.util.Shell.runCommand(Shell.java:404)
    at org.apache.hadoop.util.Shell.run(Shell.java:379)
    at org.apache.hadoop.util.Shell$ShellCommandExecutor.execute(Shell.java:589)
    at org.apache.hadoop.util.Shell.execCommand(Shell.java:678)
    at org.apache.hadoop.util.Shell.execCommand(Shell.java:661)
    at org.apache.hadoop.fs.RawLocalFileSystem.setPermission(RawLocalFileSystem.java:639)
    at org.apache.hadoop.fs.FilterFileSystem.setPermission(FilterFileSystem.java:468)
    at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:456)
    at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:424)
    at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:905)
    at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:798)
    at org.apache.hadoop.mapred.TextOutputFormat.getRecordWriter(TextOutputFormat.java:123)
    at org.apache.spark.SparkHadoopWriter.open(SparkHadoopWriter.scala:90)
    at org.apache.spark.rdd.PairRDDFunctions$$anonfun$saveAsHadoopDataset$1$$anonfun$13.apply(PairRDDFunctions.scala:1104)
    at org.apache.spark.rdd.PairRDDFunctions$$anonfun$saveAsHadoopDataset$1$$anonfun$13.apply(PairRDDFunctions.scala:1095)
    at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:63)
    at org.apache.spark.scheduler.Task.run(Task.scala:70)
    at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:213)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

15/06/23 18:25:27 ERROR TaskSetManager: Task 0 in stage 1.0 failed 1 times; aborting job
15/06/23 18:25:27 INFO TaskSchedulerImpl: Removed TaskSet 1.0, whose tasks have all completed, from pool 
15/06/23 18:25:27 INFO TaskSchedulerImpl: Cancelling stage 1
15/06/23 18:25:27 INFO DAGScheduler: ResultStage 1 (saveAsTextFile at TestSpark.java:40) failed in 0.249 s
15/06/23 18:25:28 INFO DAGScheduler: Job 0 failed: saveAsTextFile at TestSpark.java:40, took 0.952286 s
Exception in thread "main" org.apache.spark.SparkException: Job aborted due to stage failure: Task 0 in stage 1.0 failed 1 times, most recent failure: Lost task 0.0 in stage 1.0 (TID 1, localhost): java.lang.NullPointerException
    at java.lang.ProcessBuilder.start(ProcessBuilder.java:1012)
    at org.apache.hadoop.util.Shell.runCommand(Shell.java:404)
    at org.apache.hadoop.util.Shell.run(Shell.java:379)
    at org.apache.hadoop.util.Shell$ShellCommandExecutor.execute(Shell.java:589)
    at org.apache.hadoop.util.Shell.execCommand(Shell.java:678)
    at org.apache.hadoop.util.Shell.execCommand(Shell.java:661)
    at org.apache.hadoop.fs.RawLocalFileSystem.setPermission(RawLocalFileSystem.java:639)
    at org.apache.hadoop.fs.FilterFileSystem.setPermission(FilterFileSystem.java:468)
    at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:456)
    at org.apache.hadoop.fs.ChecksumFileSystem.create(ChecksumFileSystem.java:424)
    at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:905)
    at org.apache.hadoop.fs.FileSystem.create(FileSystem.java:798)
    at org.apache.hadoop.mapred.TextOutputFormat.getRecordWriter(TextOutputFormat.java:123)
    at org.apache.spark.SparkHadoopWriter.open(SparkHadoopWriter.scala:90)
    at org.apache.spark.rdd.PairRDDFunctions$$anonfun$saveAsHadoopDataset$1$$anonfun$13.apply(PairRDDFunctions.scala:1104)
    at org.apache.spark.rdd.PairRDDFunctions$$anonfun$saveAsHadoopDataset$1$$anonfun$13.apply(PairRDDFunctions.scala:1095)
    at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:63)
    at org.apache.spark.scheduler.Task.run(Task.scala:70)
    at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:213)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

Driver stacktrace:
    at org.apache.spark.scheduler.DAGScheduler.org$apache$spark$scheduler$DAGScheduler$$failJobAndIndependentStages(DAGScheduler.scala:1266)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage$1.apply(DAGScheduler.scala:1257)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage$1.apply(DAGScheduler.scala:1256)
    at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
    at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
    at org.apache.spark.scheduler.DAGScheduler.abortStage(DAGScheduler.scala:1256)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed$1.apply(DAGScheduler.scala:730)
    at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed$1.apply(DAGScheduler.scala:730)
    at scala.Option.foreach(Option.scala:236)
    at org.apache.spark.scheduler.DAGScheduler.handleTaskSetFailed(DAGScheduler.scala:730)
    at org.apache.spark.scheduler.DAGSchedulerEventProcessLoop.onReceive(DAGScheduler.scala:1450)
    at org.apache.spark.scheduler.DAGSchedulerEventProcessLoop.onReceive(DAGScheduler.scala:1411)
    at org.apache.spark.util.EventLoop$$anon$1.run(EventLoop.scala:48)
15/06/23 18:25:28 INFO SparkContext: Invoking stop() from shutdown hook
15/06/23 18:25:28 INFO SparkUI: Stopped Spark web UI at http://10.37.145.179:4040
15/06/23 18:25:28 INFO DAGScheduler: Stopping DAGScheduler
15/06/23 18:25:28 INFO MapOutputTrackerMasterEndpoint: MapOutputTrackerMasterEndpoint stopped!
15/06/23 18:25:28 INFO Utils: path = C:\Users\crh537\AppData\Local\Temp\spark-a52371d8-ae6a-4567-b759-0a6c66c1908c\blockmgr-4d17a5b4-c8f8-4408-af07-0e88239794e8, already present as root for deletion.
15/06/23 18:25:28 INFO MemoryStore: MemoryStore cleared
15/06/23 18:25:28 INFO BlockManager: BlockManager stopped
15/06/23 18:25:28 INFO BlockManagerMaster: BlockManagerMaster stopped
15/06/23 18:25:28 INFO SparkContext: Successfully stopped SparkContext
15/06/23 18:25:28 INFO Utils: Shutdown hook called

此致Shankar

Answer 1

您可以使用coalesce方法保存到单个文件中。这样，您的代码将如下所示：

val myFile = sc.textFile("file.txt")
val finalRdd = doStuff(myFile)
finalRdd.coalesce(1).saveAsTextFile("newfile")

还有另一种方法repartition可以执行相同的操作，但是它将导致洗牌，这可能会非常昂贵，而合并会尝试避免洗牌。