我想把rdd的效率和通常的相比 List 在斯卡拉Spark。

val list = Range(1, 1000000, 1)
val dist_list = sc.parallelize(list)

val start_time = System.nanoTime
val sum = list.reduce((x,y) => x+y)
println(s"for list time is      ${System.nanoTime - start_time}")

val s_time = System.nanoTime
val dist_sum = dist_list.reduce((x,y) => x+y)
println(s"for dist_list time is ${System.nanoTime - s_time}")

结果呢

for list time is      24849500
for dist_list time is 378051900

这意味着rdd比通常的操作慢15倍。为什么会这样？