这是因为服务器上设置的应用程序环境越来越多，也可能因为进一步分派当前任务以隔离责任。
This could be because more application environments are being placed on the server, or because of splitting the delegation of currents tasks down further to segregate responsibility.
白盒子是可互相交换的，主应用程序可能把集群中的任何机器指派为控制者，而这个机器就把map和reduce任务分派给其它连接的白盒子。
White boxes are interchangeable, and the main application may assign any machine in the cluster as the controller, and this one in turn assigns map or reduce tasks to other connected white boxes.
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