api.java
该包用于java编程时
JavaDoubleRDD
将scala Double 转java Double
注意一行代码：import java.lang.{Double => JDouble}
scala语法起了个类的别名
而java也有类似的，如import com.example.Calendar as MyCalendar
broadcast
keep a read-only variable cached on each machine rather than tasks
TorrentBroadcast
driver将广播对象切成small chunks
避免driver单点分发成为瓶颈，executor从driver的BlockManager取到数据后可以供其他executor获取
deploy
提交任务
rdd
CoalescedRDD
DefaultPartitionCoalescer
locality information
Manhua
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