V$system_event中Wait事件的一段話和resources_wait.sql

V$SYSTEM_EVENT shows the total number of waits and timeouts, and the total

waiting time recorded for each type of event, accumulated for all processes over

the life of the instance. It is normal to order the events waited for in descending

order of the total time waited, as an indicator of the potential severity of each

type of wait.

However, the total time waited is really only meaningful for those that indicate

waiting for resources. If processes have been waiting because they have no work

to do, then the time waited is immaterial. If they have been waiting for routine

operations, such as disk I/O, then the total time waited will depend on the

workload. In such cases, the average time waited is much more interesting than

the total time waited.

This classification of wait types into idle waits, routine waits, and resource waits

is vital to a correct understanding of the wait statistics. Accordingly, APT has

separate scripts for resource waits and routine waits, and ignores idle waits

altogether. The routine_waits.sql script shows only the average time waited for

each type of routine wait. The resource_waits.sql script (see Example 2.1) shows

the types of resources waited for in descending order of the total time waited, but

also shows the average time waited.

resources_wait.sql:

-------------------------------------------------------------------------------
--
-- Script:	resource_waits.sql
-- Purpose:	to show the total waiting time for resource types
--
-- Copyright:	(c) 1998 Ixora Pty Ltd
-- Author:	Steve Adams
--
-------------------------------------------------------------------------------
@reset_sqlplus

column average_wait format 9999990.00

select
  substr(e.event, 1, 40)  event,
  e.time_waited,
  e.time_waited / (
    e.total_waits - decode(e.event, 'latch free', 0, e.total_timeouts)
  )  average_wait
from
  sys.v_$system_event  e,
  sys.v_$instance  i
where
  e.event = 'buffer busy waits' or
  e.event = 'enqueue' or
  e.event = 'free buffer waits' or
  e.event = 'global cache freelist wait' or
  e.event = 'latch free' or
  e.event = 'log buffer space' or
  e.event = 'parallel query qref latch' or
  e.event = 'pipe put' or
  e.event = 'write complete waits' or
  e.event like 'library cache%' or
  e.event like 'log file switch%' or
  ( e.event = 'row cache lock' and
    i.parallel = 'NO'
  )
union all
select
  'non-routine log file syncs',
  round(e.average_wait * greatest(e.total_waits - s.value, 0)),
  e.average_wait
from
  sys.v_$system_event e,
  sys.v_$sysstat s
where
  e.event = 'log file sync' and
  s.name = 'user commits'
order by
  2 desc
/

@reset_sqlplus
其中和reset_sqlplus是：
       
-------------------------------------------------------------------------------
--
-- Script:	reset_sqlplus.sql
-- Purpose:	to reset sqlplus settings
--
-- Copyright:	(c) 1998 Ixora Pty Ltd
-- Author:	Steve Adams
--
-------------------------------------------------------------------------------

clear breaks
clear columns
clear computes
set feedback off
set verify off

      
        
資料來源：Oracle8i Internal Services