ITPub博客

首页 > Linux操作系统 > Linux操作系统 > latch (Understanding the spin statistics)

latch (Understanding the spin statistics)

原创 Linux操作系统 作者:v_fantasy 时间:2009-02-25 15:17:48 0 删除 编辑

The latch statistics in the V$LATCH family of views record a get whenever a
process acquires a latch in willing-to-wait mode. If the process fails to get the
latch without spinning, a miss is recorded. If the latch is obtained after one or
more spin iterations, a spin get is recorded. If the latch cannot be obtained while
spinning, the process relinquishes the CPU and enters a sleep. No matter how
many times the process subsequently wakes up, spins, and sleeps again, no
further gets or misses will be recorded, and neither will a spin get be recorded if
the latch is finally obtained while spinning. So, the number of times that a latch
was obtained without spinning at all is gets - misses. I call these simple gets. The
APT script. latch_gets.sql shows the breakdown of gets into simple gets, spin
gets, and gets that slept, called sleep gets.

 

 


column name        format a30 heading "LATCH TYPE"  trunc
column simple_gets format a18 heading "SIMPLE GETS" justify right
column spin_gets   format a14 heading "SPIN GETS"   justify right
column sleep_gets  format a14 heading "SLEEP GETS"  justify right

select
  l.name,
  substr(
    to_char(
      l.gets - l.misses,
      '9999999990'
    ),
    2
  ) ||
  ' ' ||
  substr(
    to_char(
      100 * (l.gets - l.misses) / l.gets,
      '999.00'
    ),
    2
  ) ||
  '%'  simple_gets,
  substr(
    to_char(
      l.spin_gets,
      '9999990'
    ),
    2
  ) ||
  ' ' ||
  substr(
    to_char(
      100 * l.spin_gets / l.gets,
      '90.00'
    ),
    2
  ) ||
  '%'  spin_gets,
  substr(
    to_char(
      l.misses - l.spin_gets,
      '9999990'
    ),
    2
  ) ||
  ' ' ||
  substr(
    to_char(
      100 * (l.misses - l.spin_gets) / l.gets,
      '90.00'
    ),
    2
  ) ||
  '%'  sleep_gets
from
  sys.v_$latch  l
where
  l.gets > 0
order by
  l.name

来自 “ ITPUB博客 ” ,链接:http://blog.itpub.net/16158219/viewspace-557742/,如需转载,请注明出处,否则将追究法律责任。

上一篇: constraint states
请登录后发表评论 登录
全部评论

注册时间:2008-10-07

  • 博文量
    98
  • 访问量
    180300