v$session_event , v$system_event , v$session_wait

v$session_event , v$session_wait

http://hi.baidu.com/linuxocp/blog/item/daef1013cadf72caa7ef3f15.html

(1)-V$SESSION_WAIT

　　這是一個尋找效能瓶頸的關鍵檢視。它提供了任何情況下session在資料庫中當前正在等待什麼(如果session當前什麼也沒在做，則顯示它最後的等待事件)。當系統存在效能問題時，本檢視可以做為一個起點指明探尋問題的方向。

　　V$SESSION_WAIT中，每一個連線到例項的session都對應一條記錄。

v$system_event :

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

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