广播变量

1. 广播变量有个要求，广播变量是只读的，分区中只能获取广播变量的值，无法更改广播变量的值
2. 优势：节省了磁盘io，数据量越大，效果越明显
3. 使用：直接通过广播变量的.value函数获取广播变量的值
4. 案例

package videovar

import org.apache.spark.rdd.RDD
import org.apache.spark.{SparkConf, SparkContext}

object VideoVar {
  def main(args: Array[String]): Unit = {
    val sparkConf = new SparkConf().setMaster("local[2]").setAppName("sum")
    val sc = new SparkContext(sparkConf)
    val rdd: RDD[Int] = sc.makeRDD(1 to 100)

    var num = 3;
    val broadcast = sc.broadcast(num)
    val filter1: RDD[Int] = rdd.filter((num: Int) => {
      if (num % broadcast.value == 0) {
        true
      } else {
        false
      }
    })
    val filter2: RDD[Int] = rdd.filter((num: Int) => {
      if (num % (broadcast.value*broadcast.value) == 0) {
        true
      } else {
        false
      }
    })
    val str1: String = filter1.collect().mkString(",")
    val str2: String = filter2.collect().mkString(",")
    println(str1)
    println(str2)
    sc.stop()
  }
}