访问BroadCasted数据框时获取Null指针异常 [英] Getting Null pointer exception while accessing BroadCasted Dataframe

问题描述

广播数据帧并尝试在Spark UDF中访问它们时，我得到了Null指针异常.

I am getting Null pointer exception when broadcasting a Dataframe and trying to access them in a Spark UDF.

UDF定义-

def test_udf(parm1: String,  parm2: String,  paarm3: String,  ) = {
println ("Inside UDF ")           
B.value.take(1).foreach { println }
println("after print") 

... .......}

..... ....... }

> sqlContext.udf.register("test_udf", test_udf _)

广播-

val B = sc.broadcast(sqlContext.sql("""Select * FROM table_a where col1='10102'""")) // Returns almost 20 MB data

访问UDF-

val df = sqlContext.sql("SELECT test_udf(parm1,parm2,parm3) AS test FROM table_b").take(1)

此行之后，我在B行以下的UDF中得到空指针异常.value.take(1).foreach {println}

After this line i am getting null pointer exception in UDF at below line B.value.take(1).foreach { println }

我怀疑广播无法正确进行.这段代码有问题吗?使用Spark 1.6.1

I am suspecting that Broadcast is not happening correctly. Is it something wrong in this code? Using Spark 1.6.1

推荐答案

您收到一个异常，因为它不是有效的Spark程序:

You get an exception because it is not a valid Spark program:

• 广播DataFrame对象不是有意义的操作.这就是为什么我们具有广播加入提示.
• Spark不支持对分布式数据结构的嵌套操作.换句话说，您无法在UDF中访问DataFrame.

• broadcasting DataFrame object is not a meaningful operation. This is why we have broadcast join hints.
• Spark doesn't support nested operations on distributed data structure. In other words you cannot access DataFrame inside an UDF.

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