spark-broadcast in spark

  go through this block codes below,we will figure out some conclusions:

val barr1 = sc.broadcast(arr1) //-broadcast a array with 1M int elements
      //-this is a embedded broadcast wrapped by rdd below.so this data
      val observedSizes = sc.parallelize(1 to 10, slices).map(_ => barr1.value.size)  //-embeded broadcast
      // Collect the small RDD so we can print the observed sizes locally.
      observedSizes.collect().foreach(i => println(i))

 

 note:

1.if there is a embeded broadcast in a rdd,the bc will be deserialized with the same process of rdd deserialization.(this procedure is not present in this figure)

2.so  a bottleneck will occur in driver when all the executors try to fetch out block data simetaneously from driver at first time.

refer:

Spark源码系列（五）分布式缓存