E.wait_class 'Idle'

Question

Hi,
I'm following this article :
http://www.dba-oracle.com/oracle10g_tuning/t_waits_events_signatures.htm
And there is a query : ash_user_wait_time.sql
select
   s.sid,
   s.username,
   sum(h.wait_time + h.time_waited ) "total wait time"
from
   v$active_session_history     h,
   v$session                  s,
   v$event_name                  e
where
   h.session_id = s.sid
and
   e.event_id = h.event_id
and
   e.wait_class <> 'Idle'
and
   s.username IS NOT NULL
group by
   s.sid, s.username
order by 3;But it shows the Idle sessions also even if e.wait_class is different from 'Idle'.
To show thatI modified it to :
select
   s.sid,
   s.username,
   s.wait_class,
   sum(h.wait_time + h.time_waited ) "total wait time"
from
   v$active_session_history     h,
   v$session                  s,
   v$event_name                  e
where
   h.session_id = s.sid
and
   e.event_id = h.event_id
and
   e.wait_class <> 'Idle'
and
   s.username IS NOT NULL
group by
   s.sid, s.username, s.wait_class
order by 4;The result for me is :
       SID USERNAME   WAIT_CLASS total wait time
       139 USER1      Idle                 14328
       145 USER1      Idle                 21075
       159 USER1      Idle                270668
       140 USER2      Idle               1515525
       136 USER1      Idle               2374375I do not see the interest of e.wait_class <> 'Idle' condition. And the result of query without this condition is the same.
Any idea ? Thank you.

Answer 1

Because you need to suppress the idle event class, as idle events are events like 'Sqlnet message from client': they are inevitable, everyone will have them, and they usually can not be tuned.
Sybrand Bakker
Senior Oracle DBA