为什么当我使用扩展应用程序时,火花广播无法正常工作? [英] Why spark broadcast doesn't work well when I use extends App?
问题描述
第一个代码引发空指针异常。
object TryBroadcast扩展App {
val conf = new SparkConf( ).setAppName( o_o)
val sc = new SparkContext(conf)
val sample = sc.parallelize(1至1024)
val bro = sc.broadcast(6666)
val broSample = sample.map(x => x.toString + bro.value)
broSample.collect()。foreach(println)
}
第二个效果很好。
object TryBroadcast {
def main(args:Array [String]){
val conf = new SparkConf()。setAppName( o_o)
val sc = new SparkContext(conf)
val sample = sc.parallelize(1到1024)
val bro = sc.broadcast(6666)
val broSample = sample.map(x => x.toString + bro.value)
broSample.collect()。foreach(println)
}
}
scala版本:2.10.5
spa rk版本:1.4.0
stackTrace:
lang.NullPointerException
在TryBroadcast $$ anonfun $ 1。 apply(TryBroadcast.scala:11)
在TryBroadcast $$ anonfun $ 1.apply(TryBroadcast.scala:11)
在scala.collection.Iterator $$ anon $ 11.next(Iterator.scala:328)
在scala.collection.Iterator $ class.foreach(Iterator.scala:727)
在scala.collection.AbstractIterator.foreach(Iterator.scala:1157)
在scala.collection.generic .scalable.growable $ class。$ plus $ plus $ eq(Growable.scala:48)
在scala.collection.mutable.ArrayBuffer。$ plus $ plus $ eq(ArrayBuffer.scala:103)
在scala .collection.mutable.ArrayBuffer。$ plus $ plus $ eq(ArrayBuffer.scala:47)
在scala.collection.TraversableOnce $ class.to(TraversableOnce.scala:273)
在scala.collection。在scala.collection.TraversableOnce $ class.toBuffer(TraversableOnce.scala:265)
在scala.collection.AbstractIterator.toBuffer(Iterator.scala)上的AbstractIterator.to(Iterator.scala:1157)
:1157)在scala.collection.TraversableOnce $ class.toArray(TraversableOnce.scala:252)
在scala.collection.AbstractIterator.toArray(Iterator.scala:1157)
在org。 apache.spark.rdd.RDD $$ anonfun $ collect $ 1 $$ anonfun $ 12.apply(RDD.scala:885)
在org.apache.spark.rdd.RDD $$ anonfun $ collect $ 1 $ anonfun $ 12 .apply(RDD.scala:885)
在org.apache.spark.SparkContext $$ anonfun $ runJob $ 5.apply(SparkContext.scala:1765)
在org.apache.spark.SparkContext $$ anonfun $ runJob $ 5.apply(SparkContext.scala:1765)
在org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:63)
在org.apache.spark.scheduler.Task .run(Task.scala:70)
在org.apache.spark.executor.Executor $ TaskRunner.run(Executor.scala:213)
在java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor .java:1142)java.util.concurrent.ThreadPoolExecutor $ Worker.run(ThreadPoolExecutor.java:617)
java.lang.Thread.run(Thread.java:745)
bro
完全不同。在第一个实例中,它是单例类实例( TryBroadcast
)上的一个字段。在第二个变量中,它是一个局部变量。
该局部变量被捕获,序列化并发送给执行者。在第一种情况下,引用是针对字段的,因此单例将被捕获并发送。我不确定Scala单例的构建方式和捕获方式。显然,在这种情况下,它在执行程序上访问时最终未初始化。
您可以将 bro
设为本地像这样的变量:
object TryBroadcast扩展了应用{{b $ b val conf = new SparkConf()。setAppName( o_o )
val sc =新的SparkContext(conf)
val sample = sc.parallelize(1至1024)
val broSample = {
val bro = sc.broadcast(6666)
sample.map(x => x.toString + bro.value)
}
broSample.collect()。foreach(println)
}
The first code throws null pointer exception.
object TryBroadcast extends App{
val conf = new SparkConf().setAppName("o_o")
val sc = new SparkContext(conf)
val sample = sc.parallelize(1 to 1024)
val bro = sc.broadcast(6666)
val broSample = sample.map(x => x.toString + bro.value)
broSample.collect().foreach(println)
}
The second works well.
object TryBroadcast {
def main(args: Array[String]) {
val conf = new SparkConf().setAppName("o_o")
val sc = new SparkContext(conf)
val sample = sc.parallelize(1 to 1024)
val bro = sc.broadcast(6666)
val broSample = sample.map(x => x.toString + bro.value)
broSample.collect().foreach(println)
}
}
It seems spark broadcast has something conflict with scala.App
scala version: 2.10.5 spark version: 1.4.0 stackTrace:
lang.NullPointerException
at TryBroadcast$$anonfun$1.apply(TryBroadcast.scala:11)
at TryBroadcast$$anonfun$1.apply(TryBroadcast.scala:11)
at scala.collection.Iterator$$anon$11.next(Iterator.scala:328)
at scala.collection.Iterator$class.foreach(Iterator.scala:727)
at scala.collection.AbstractIterator.foreach(Iterator.scala:1157)
at scala.collection.generic.Growable$class.$plus$plus$eq(Growable.scala:48)
at scala.collection.mutable.ArrayBuffer.$plus$plus$eq(ArrayBuffer.scala:103)
at scala.collection.mutable.ArrayBuffer.$plus$plus$eq(ArrayBuffer.scala:47)
at scala.collection.TraversableOnce$class.to(TraversableOnce.scala:273)
at scala.collection.AbstractIterator.to(Iterator.scala:1157)
at scala.collection.TraversableOnce$class.toBuffer(TraversableOnce.scala:265)
at scala.collection.AbstractIterator.toBuffer(Iterator.scala:1157)
at scala.collection.TraversableOnce$class.toArray(TraversableOnce.scala:252)
at scala.collection.AbstractIterator.toArray(Iterator.scala:1157)
at org.apache.spark.rdd.RDD$$anonfun$collect$1$$anonfun$12.apply(RDD.scala:885)
at org.apache.spark.rdd.RDD$$anonfun$collect$1$$anonfun$12.apply(RDD.scala:885)
at org.apache.spark.SparkContext$$anonfun$runJob$5.apply(SparkContext.scala:1765)
at org.apache.spark.SparkContext$$anonfun$runJob$5.apply(SparkContext.scala:1765)
at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:63)
at org.apache.spark.scheduler.Task.run(Task.scala:70)
at org.apache.spark.executor.Executor$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)
bro
in the two cases is quite different. In the first one it's a field on a singleton class instance (TryBroadcast
). In the second one it is a local variable.
I the local variable gets captured, serialized and sent over to the executors. In the first case the reference is to a field, so the singleton would get captured and sent. I'm not sure how a Scala singleton is built and how it is captured. Apparently in this case it ends up uninitialized when it is accessed on the executor.
You could make bro
a local variable like this:
object TryBroadcast extends App {
val conf = new SparkConf().setAppName("o_o")
val sc = new SparkContext(conf)
val sample = sc.parallelize(1 to 1024)
val broSample = {
val bro = sc.broadcast(6666)
sample.map(x => x.toString + bro.value)
}
broSample.collect().foreach(println)
}
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