对视图V$SESSION_WAIT和V$PX_SESSION的部分字段解释

V$SESSION_WAIT

WAIT_CLASS_IDNUMBERIdentifier of the class of the wait eventWAIT_CLASS#NUMBERNumber of the class of the wait eventWAIT_CLASSVARCHAR2(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_GROUPNUMBERThe logical group of servers to which this cluster database process belongsSERVER_SETNUMBERThe logical set of servers to which this cluster database process belongs. A single server group will have at most two server sets.SERVER#NUMBERThe 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。