V$SESSION_WAIT

`WAIT_CLASS_ID`	`NUMBER`	Identifier of the class of the wait event
`WAIT_CLASS#`	`NUMBER`	Number of the class of the wait event
`WAIT_CLASS`	`VARCHAR2(64)`	Name of the class of the wait event

注释：

WAIT_CLASS_ID

，表示该等待事件在整个等待事件这个范围上的编号

WAIT_CLASS#

，表示该等待事件在该会话下的编号，即V$SESSION_WAIT视图里的第几行

V$PX_SESSION

`SERVER_GROUP`	`NUMBER`	The logical group of servers to which this cluster database process belongs
`SERVER_SET`	`NUMBER`	The logical set of servers to which this cluster database process belongs. A single server group will have at most two server sets.
`SERVER#`	`NUMBER`	The logical number of the cluster database process within a server set

注释：

一个并行查询可以由多个DFO tree组成，一个DFO tree对应为一个group（即V$PX_SESSION视图中的

SERVER_GROUP

字段），一个group则由多个set（即V$PX_SESSION视图中的

SERVER_SET

字段）组成，一个group至多由2个set构成。

SERVER#

，表示一个set里并行服务器进程的编号。