Flink Dataset Api（六）广播变量

原文链接： https://www.cnblogs.com/niutao/p/10548481.html

Flink支持广播变量，就是将数据广播到具体的taskmanager上，数据存储在内存中，这样可以减缓大量的shuffle操作；

比如在数据join阶段，不可避免的就是大量的shuffle操作，我们可以把其中一个dataSet广播出去，一直加载到taskManager的内存中，可以直接在内存中拿数据，避免了大量的shuffle，导致集群性能下降；

注意：因为广播变量是要把dataset广播到内存中，所以广播的数据量不能太大，否则会出现OOM这样的问题

Broadcast：Broadcast是通过withBroadcastSet(dataset，string)来注册的

Access：通过getRuntimeContext().getBroadcastVariable(String)访问广播变量

import org.apache.flink.api.common.functions.RichMapFunction
import org.apache.flink.configuration.Configuration
import scala.collection.mutable
import scala.collection.mutable.{ArrayBuffer,}
import scala.util.Random

object SourceTest {
  def main(args: Array[String]): Unit = {
    import org.apache.flink.api.scala.extensions._
    import org.apache.flink.api.scala._
    import org.apache.flink.streaming.api.scala.extensions._

    val env = ExecutionEnvironment.getExecutionEnvironment

    //TODO data2  join  data3的数据，使用广播变量完成
    val data2 = new mutable.MutableList[(Int, Long, String)]
    data2.+=((1, 1L, "Hi"))
    data2.+=((2, 2L, "Hello"))
    data2.+=((3, 2L, "Hello world"))
    val ds1 = env.fromCollection(Random.shuffle(data2))
    val data3 = new mutable.MutableList[(Int, Long, Int, String, Long)]
    data3.+=((1, 1L, 0, "Hallo", 1L))
    data3.+=((2, 2L, 1, "Hallo Welt", 2L))
    data3.+=((2, 3L, 2, "Hallo Welt wie", 1L))
    val ds2 = env.fromCollection(Random.shuffle(data3))

    //todo 使用内部类RichMapFunction，提供open和map，可以完成join的操作
    val result = ds1.map(new RichMapFunction[(Int , Long , String) , 
                    ArrayBuffer[(Int , Long , String , String)]] {

      var brodCast:mutable.Buffer[(Int, Long, Int, String, Long)] = null

      override def open(parameters: Configuration): Unit = {
        import scala.collection.JavaConverters._
        //asScala需要使用隐式转换
        brodCast = this.getRuntimeContext.getBroadcastVariable[(Int, Long, Int, String, 
                    Long)]("ds2").asScala
      }
      override def map(value: (Int, Long, String)):ArrayBuffer[(Int , Long , String , String)] = {
        val toArray: Array[(Int, Long, Int, String, Long)] = brodCast.toArray
        val array = new mutable.ArrayBuffer[(Int , Long , String , String)]
        var index = 0

        var a:(Int, Long, String, String) = null
        while(index < toArray.size){
          if(value._2 == toArray(index)._5){
            a = (value._1 , value._2 , value._3 , toArray(index)._4)
            array += a
          }
          index = index + 1
        }
        array
      }
    }).withBroadcastSet(ds2 , "ds2")
    println(result.collect())
  }
}