1. Anar Godjaev
http://anargodjaev.wordpress.com/
Oracle Wait Interface (OWI)
Oracle wait interface is a group of views that you can use to monitorwaiting
events and sessions waiting them.
1- first thing is thinking system wide.
--- System wide event waits
-select* from v$system_eventorder by total_waitsdesc;
--select* from v$event_name;
2- and then session wide
-- Session wide events
--- you can see the SID and easily join with v$session
select* from v$session_eventorder by total_waitsdesc;
3- time to examine session waits currently
--- session wide waits
--- you can obtain P1, P2 and P3 parameter meanings in v$event_name
select* from v$session_waitorder by seconds_in_waitdesc;
NOTES
N1- P1, P2 and P3 columns are important in some types of waits. Forexample:
If (event_name IN
(„db file sequential read‟ , „db file scattered read‟))
then
P1 means file#
P2 means block#
P3 means blocks
End If;
--- lets find sessions waiting the files
-select
t1.event,
t1.state,
t1.wait_time,
t1.seconds_in_wait,
t2.username,
t3.name
from
v$session_wait t1,
v$session t2,

2. Anar Godjaev
http://anargodjaev.wordpress.com/
v$datafile t3
where
t1.sid = t2.sid and
t1.p1 = t3.file# and
t1.eventin ('db file sequential read','db file scattered read');
N2- There are two columns indicationg the waited time. “wait_time” and
“second_in_wait”. You can consider these values by reading “state” column.
If (“state” = WAITING) then
Consider “SECONDS_IN_WAIT”
Else If (“state” = WAITED_KNOWN_TIME) then
Consider “WAIT_TIME”
Else If (“state” = WAITED_UNKNOWN_TIME) then
Alter system set timed_statistics=TRUE -- 
End If
4- you can also examine system wide and session wide statistics
--- system statistics
-select* from v$sysstat;
--- session statistics
--- you cannot find statistics name in v$sesstat
-- so we have to join with v$statname
select
t1.sid,
t3.username,
t2.name,
t1.value
from
v$sesstat t1,
v$statname t2,
v$session t3
where
t1.statistic# = t2.statistic# and
t1.sid = t3.sid and
t3.usernameis not null;
---select* from v$statname;
List of views
v$system_event
System wide wait events.
Values are total waits until system startup.
Wait values are reset every system restart.
v$event_name
Properties of wait events.
v$session_event

3. Anar Godjaev
http://anargodjaev.wordpress.com/
Session wide wait events.
Has almost same properties with v$system_event.
There is one mor column for SID.
v$session_wait
Session wide waits, this view gives you the currents waits byuser and resets
every session kills itself.
v$latch
v$latchname
v$enqueue
v$sysstat
v$sesstat
v$filestat
v$tempstat
v$sgastat
v$pgastat
v$statname
parameters
timed_statistics
statistics_level
some of the important wait events (non idle wait events)
buffer busy waits
db file scattered read
db file sequential read
enqueue
free buffer waits
latch free
log file parallel write
log file sync
NOTES
These kind of events points:
Inefficient sql.
Inefficient system architecture.
Inproper instance confugiration.
Some of the idle events (can be ignored most of the times)
NULL
SQL*NET Message
Rdbmsipc message
Pmon timer
Pipe get
Smon timer
NOTES
Not an indiaction of performance problem.
Some of the important statistics
bytes received via SQL*Net from client
bytes sent via SQL*Net to client
consistent gets --consistent gets+db block gets =logical IO