Spark block replica设置(Rank设置)

block replica默认随机存储：

BlockManager.scala def initialize(appId: String): Unit = 

val priorityClass = conf.get("spark.storage.replication.policy", classOf[RandomBlockReplicationPolicy].getName)

replication policy在BlockReplicationPolicy.scala中定义，如果是hdfs，需要配置成BasicBlockReplicationPolicy，一份在rank，一份在out of rank，其它随机选择。

Spark rank配置（TopologyMapper.scala）：

spark.storage.replication.topologyMapper配置map 类：

org.apache.spark.storage.FileBasedTopologyMapper和DefaultTopologyMapper（无topo设置，默认配置项）

spark.storage.replication.topologyFile配置map config，为java properties配置文档