在整个shuffle阶段,内存像一个连续的Longs数组(128M的大块,请查看see https://github.com/apache/spark/blob/branch-1.4/core/src/main/scala/org/apache/spark/shuffle/ShuffleMemoryManager.scala through https://github.com/apache/spark/blob/branch-1.4/core/src/main/java/org/apache/spark/shuffle/unsafe/Un...