在Scala Apache Spark中输出DStream的内容

时间：2015-03-12 12:32:36

标签： scala apache-spark

Spark代码下面似乎没有对文件example.txt

执行任何操作 
val conf = new org.apache.spark.SparkConf()
  .setMaster("local")
  .setAppName("filter")
  .setSparkHome("C:\\spark\\spark-1.2.1-bin-hadoop2.4")
  .set("spark.executor.memory", "2g");

val ssc = new StreamingContext(conf, Seconds(1))
val dataFile: DStream[String] = ssc.textFileStream("C:\\example.txt")

dataFile.print()
ssc.start() // Start the computation
ssc.awaitTermination() // Wait for the computation to terminate

我尝试使用dataFile.print()

打印文件的前10个元素

部分生成的输出：

15/03/12 12:23:53 INFO JobScheduler: Started JobScheduler
15/03/12 12:23:54 INFO FileInputDStream: Finding new files took 105 ms
15/03/12 12:23:54 INFO FileInputDStream: New files at time 1426163034000 ms:

15/03/12 12:23:54 INFO JobScheduler: Added jobs for time 1426163034000 ms
15/03/12 12:23:54 INFO JobScheduler: Starting job streaming job 1426163034000 ms.0 from job set of time 1426163034000 ms
-------------------------------------------
Time: 1426163034000 ms
-------------------------------------------

15/03/12 12:23:54 INFO JobScheduler: Finished job streaming job 1426163034000 ms.0 from job set of time 1426163034000 ms
15/03/12 12:23:54 INFO JobScheduler: Total delay: 0.157 s for time 1426163034000 ms (execution: 0.006 s)
15/03/12 12:23:54 INFO FileInputDStream: Cleared 0 old files that were older than 1426162974000 ms: 
15/03/12 12:23:54 INFO ReceivedBlockTracker: Deleting batches ArrayBuffer()
15/03/12 12:23:55 INFO FileInputDStream: Finding new files took 2 ms
15/03/12 12:23:55 INFO FileInputDStream: New files at time 1426163035000 ms:

15/03/12 12:23:55 INFO JobScheduler: Added jobs for time 1426163035000 ms
15/03/12 12:23:55 INFO JobScheduler: Starting job streaming job 1426163035000 ms.0 from job set of time 1426163035000 ms
-------------------------------------------
Time: 1426163035000 ms
-------------------------------------------

15/03/12 12:23:55 INFO JobScheduler: Finished job streaming job 1426163035000 ms.0 from job set of time 1426163035000 ms
15/03/12 12:23:55 INFO JobScheduler: Total delay: 0.011 s for time 1426163035000 ms (execution: 0.001 s)
15/03/12 12:23:55 INFO MappedRDD: Removing RDD 1 from persistence list
15/03/12 12:23:55 INFO BlockManager: Removing RDD 1
15/03/12 12:23:55 INFO FileInputDStream: Cleared 0 old files that were older than 1426162975000 ms: 
15/03/12 12:23:55 INFO ReceivedBlockTracker: Deleting batches ArrayBuffer()
15/03/12 12:23:56 INFO FileInputDStream: Finding new files took 3 ms
15/03/12 12:23:56 INFO FileInputDStream: New files at time 1426163036000 ms:

example.txt的格式为：

gdaeicjdcg,194,155,98,107
jhbcfbdigg,73,20,122,172
ahdjfgccgd,28,47,40,178
afeidjjcef,105,164,37,53
afeiccfdeg,29,197,128,85
aegddbbcii,58,126,89,28
fjfdbfaeid,80,89,180,82

正如print文档所述：

/ **    *打印此DStream中生成的每个RDD的前十个元素。这是一个输出    *运算符，因此这个DStream将被注册为输出流并在那里实现。    * /

这是否意味着为此流生成了0 RDD？如果想要查看RDD的内容，则使用Apache Spark将使用RDD的collect函数。这些类似于Streams的方法吗？那么总之如何打印到Stream的控制台内容？

更新：

根据@ 0x0FFF评论更新了代码。 http://spark.apache.org/docs/1.2.0/streaming-programming-guide.html似乎没有给出从本地文件系统读取的示例。这不像使用Spark核心那样常见，其中有明确的例子来从文件中读取数据吗？

这是更新的代码：

val conf = new org.apache.spark.SparkConf()
  .setMaster("local[2]")
  .setAppName("filter")
  .setSparkHome("C:\\spark\\spark-1.2.1-bin-hadoop2.4")
  .set("spark.executor.memory", "2g");

val ssc = new StreamingContext(conf, Seconds(1))
val dataFile: DStream[String] = ssc.textFileStream("file:///c:/data/")

dataFile.print()
ssc.start() // Start the computation
ssc.awaitTermination() // Wait for the computation to terminate

但输出相同。当我将新文件添加到c:\\data目录（其格式与现有数据文件相同）时，它们不会被处理。我假设dataFile.print应首先打印10行到控制台？

更新2：

也许这与我在Windows环境中运行此代码的事实有关？

3 个答案:

答案 0 :(得分：2)

你误解了textFileStream的使用。以下是Spark文档中的描述：

创建一个输入流，监视与Hadoop兼容的文件系统以获取新文件并将其作为文本文件读取（使用密钥作为LongWritable，值为Text，输入格式为TextInputFormat）。

首先，您应该将其传递给目录，其次，此目录应该可以从运行接收器的节点获得，因此最好将HDFS用于此目的。然后，当您将 新 文件放入此目录时，它将由函数print()处理，并且将为其打印前10行

更新

我的代码：

[alex@sparkdemo tmp]$ pyspark --master local[2]
Python 2.6.6 (r266:84292, Nov 22 2013, 12:16:22) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
Spark assembly has been built with Hive, including Datanucleus jars on classpath
s15/03/12 06:37:49 WARN Utils: Your hostname, sparkdemo resolves to a loopback address: 127.0.0.1; using 192.168.208.133 instead (on interface eth0)
15/03/12 06:37:49 WARN Utils: Set SPARK_LOCAL_IP if you need to bind to another address

Welcome to
      ____              __
     / __/__  ___ _____/ /__
    _\ \/ _ \/ _ `/ __/  '_/
   /__ / .__/\_,_/_/ /_/\_\   version 1.2.0
      /_/

Using Python version 2.6.6 (r266:84292, Nov 22 2013 12:16:22)
SparkContext available as sc.
>>> from pyspark.streaming import StreamingContext
>>> ssc = StreamingContext(sc, 30)
>>> dataFile = ssc.textFileStream('file:///tmp')
>>> dataFile.pprint()
>>> ssc.start()
>>> ssc.awaitTermination()
-------------------------------------------
Time: 2015-03-12 06:40:30
-------------------------------------------

-------------------------------------------
Time: 2015-03-12 06:41:00
-------------------------------------------

-------------------------------------------
Time: 2015-03-12 06:41:30
-------------------------------------------
1 2 3
4 5 6
7 8 9

-------------------------------------------
Time: 2015-03-12 06:42:00
-------------------------------------------

答案 1 :(得分：0)

这是我编写的一个自定义接收器，用于侦听指定目录的数据：

package receivers

import java.io.File
import org.apache.spark.{ SparkConf, Logging }
import org.apache.spark.storage.StorageLevel
import org.apache.spark.streaming.{ Seconds, StreamingContext }
import org.apache.spark.streaming.receiver.Receiver

class CustomReceiver(dir: String)
  extends Receiver[String](StorageLevel.MEMORY_AND_DISK_2) with Logging {

  def onStart() {
    // Start the thread that receives data over a connection
    new Thread("File Receiver") {
      override def run() { receive() }
    }.start()
  }

  def onStop() {
    // There is nothing much to do as the thread calling receive()
    // is designed to stop by itself isStopped() returns false
  }

  def recursiveListFiles(f: File): Array[File] = {
    val these = f.listFiles
    these ++ these.filter(_.isDirectory).flatMap(recursiveListFiles)
  }

  private def receive() {

    for (f <- recursiveListFiles(new File(dir))) {

      val source = scala.io.Source.fromFile(f)
      val lines = source.getLines
      store(lines)
      source.close()
      logInfo("Stopped receiving")
      restart("Trying to connect again")

    }
  }
}

我认为需要注意的一件事是，文件需要在＆lt; = configured batchDuration的时间内处理。在下面的示例中，它设置为10秒，但如果接收器处理文件的时间超过10秒，则不会处理某些数据文件。在这一点上，我愿意纠正。

以下是自定义接收器的实现方式：

val conf = new org.apache.spark.SparkConf()
  .setMaster("local[2]")
  .setAppName("filter")
  .setSparkHome("C:\\spark\\spark-1.2.1-bin-hadoop2.4")
  .set("spark.executor.memory", "2g");

val ssc = new StreamingContext(conf, Seconds(10))

val customReceiverStream: ReceiverInputDStream[String] = ssc.receiverStream(new CustomReceiver("C:\\data\\"))

customReceiverStream.print

customReceiverStream.foreachRDD(m => {
  println("size is " + m.collect.size)
})

ssc.start() // Start the computation
ssc.awaitTermination() // Wait for the computation to terminate

更多信息： http://spark.apache.org/docs/1.2.0/streaming-programming-guide.html＆amp; https://spark.apache.org/docs/1.2.0/streaming-custom-receivers.html

答案 2 :(得分：0)

我可能发现了您的问题，您的日志中应该有这个：

WARN StreamingContext: spark.master should be set as local[n], n > 1 in local mode if you have receivers to get data, otherwise Spark jobs will not get resources to process the received data.

问题是您需要至少有 2 个内核才能运行 Spark 流应用程序。 所以解决方案应该是简单地替换：

val conf = new org.apache.spark.SparkConf()
 .setMaster("local")

作者：

val conf = new org.apache.spark.SparkConf()
  .setMaster("local[*]")

或者至少不止一个。

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