OWI Components（1）：V$SYSTEM_EVENT

V$EVENT_NAME:  当前数据库已经定义的event的数量;

V$SYSTEM_EVENT: 自动数据库实例启动到现在，oracle所有会话遇到的等待事件的aggregated statistics;
the TOTAL_TIMEOUTS column records the number of times a session failed to get the requested resource after the
initial wait.
The column TIME_WAITED reports the total amount of time spent waiting on the event.
The column AVERAGE_WAIT gives the average time for each wait and is derived from the TOTAL_WAITS and TIME_WAITED

columns.

The V$SYSTEM_EVENT view is a good place to start if you want to perform a quick health check on the database

instance. This quick health check may be helpful when you must diagnose a poorly performing database instance,

especially if you are unfamiliar with it and the application. You will quickly discover the top n bottlenecks

that plague the database instance since startup. However, don’t judge performance or make any tuning decisions

based on these bottlenecks just yet. The information is cumulative since the instance startup.
在查询视图时,我们应该关心的是时间,而不是数量.

set lines 160
set numwidth 18
col class for a15
col event for a30
col total_waits for 999,999,999
col total_timeouts for 999,999,999
col time_waited for 999,999,999,999
col average_wait for 999,999,999,999

select a.*, c.startup_time
  from v$system_event a, v$event_name b, v$instance c
 where a.event = b.name
 order by  a.time_waited;