Oracle Performance queries

 Number of Sessions Waiting On A Particular Wait Event

SELECT count(*), event
FROM v$session_wait
WHERE wait_time = 0
AND event NOT IN ('smon timer','pipe get','wakeup time manager',
'pmon timer','rdbms ipc message', 'SQL*Net message from client')
GROUP BY event
ORDER BY 1 DESC;

What Wait Events Are Sessions Waiting On

set linesize 120
col username format a10
col event format a30
 select sid, serial#,username, event,
seconds_in_wait, wait_time
from v$session where state = 'WAITING'
and wait_class != 'Idle'
order by event;

Top SQL (Buffer Gets)
This script will list the top 5 SQL statements sorted by the most number of buffer gets or logical reads

set serverout on size 1000000
declare
top5 number;
text1 varchar2(4000);
x number;
len1 number;
Cursor c1 is
select buffer_gets,substr(sql_text,1,4000)
from v$sqlarea
order by buffer_gets desc;
begin
dbms_output.put_line('Reads'||' '||' Text');
dbms_output.put_line ('-----'||' '||'---------------------------------------------------');
dbms_output.put_line(' ');
open c1;
for i in 1 .. 5 loop
fetch c1 into top5, text1;
dbms_output.put_line(rpad(to_char(top5),9)|| ' '||substr(text1,1,66));
len1 :=length(text1);
x := 66;
while len1 > x-1 loop
dbms_output.put_line('" '||substr(text1,x,64));
x := x+64;
end loop;
end loop;
end;/

Script – Top SQL (Physical Reads)
This script will list the top 5 SQL statements sorted by the most number of physical reads

set serverout on size 1000000
set feedback off
declare
top5 number;
text1 varchar2(4000);
x number;
len1 number;
Cursor c1 is
select disk_reads,substr(sql_text,1,4000)
from v$sqlarea
order by disk_reads desc;
begin
dbms_output.put_line('Reads'||' '||' Text');
dbms_output.put_line ('-----'||' '||'----------------------------------------------------');
dbms_output.put_line(' ');
open c1;
for i in 1 .. 5 loop
fetch c1 into top5, text1;
dbms_output.put_line(rpad(to_char(top5),9)|| ' '||substr(text1,1,66));
len1 :=length(text1);
x := 66;
while len1 > x-1 loop
dbms_output.put_line('" '||substr(text1,x,64));
x := x+64;
end loop;
end loop;
end;
/

Sessions with high physical reads

set linesize 120
col os_user format a10
col username format a15
col pid format 9999999999
PROMPT SESSIONS SORTED BY PHYSICAL READS
PROMPT
select
OSUSER os_user,username,
PROCESS pid,
ses.SID sid,
SERIAL#,
PHYSICAL_READS,
BLOCK_CHANGES
from v$session ses,
v$sess_io sio
where ses.SID = sio.SID
and username is not null
and status='ACTIVE'
 order by PHYSICAL_READS;

Monitor sessions with high Physical Reads

set linesize 120
col osuser format a10
col username format 10
select
OSUSER osuser,
username,
PROCESS pid,
ses.SID sid,
SERIAL#,
PHYSICAL_READS,
BLOCK_CHANGES
from v$session ses,
v$sess_io sio
where ses.SID = sio.SID
order by PHYSICAL_READS;

Monitor long running operations using v$session_longops

SELECT SID, SERIAL#, opname, SOFAR, TOTALWORK,
ROUND(SOFAR/TOTALWORK*100,2) COMPLETE
FROM V$SESSION_LONGOPS
WHERE
TOTALWORK != 0
AND SOFAR != TOTALWORK
order by 1;
Note: the same query can be used to monitor RMAN backup status
SELECT SID, SERIAL#, CONTEXT, SOFAR, TOTALWORK,
ROUND(SOFAR/TOTALWORK*100,2) "%_COMPLETE"
FROM V$SESSION_LONGOPS
WHERE OPNAME LIKE 'RMAN%'
AND OPNAME NOT LIKE '%aggregate%'
AND TOTALWORK != 0
AND SOFAR != TOTALWORK;

Locked Sessions and Locked Objects

PROMPT Blocked and Blocker Sessions
col blocker_sid format 99999999999
col blocked_sid format 99999999999
col min_blocked format 99999999999
col request format 9999999
select /*+ ORDERED */
blocker.sid blocker_sid
, blocked.sid blocked_sid
, TRUNC(blocked.ctime/60) min_blocked
, blocked.request
from (select *
from v$lock
where block != 0
and type = 'TX') blocker
, v$lock blocked
where
blocked.type='TXd blocked.block = 0
and blocked.id1 = blocker.id1;

prompt blocked objects from V$LOCK and SYS.OBJ$

set lines 132
col BLOCKED_OBJ format a35 trunc
select /*+ ORDERED */
l.sid
, l.lmode
, TRUNC(l.ctime/60) min_blocked
, u.name||'.'||o.NAME blocked_obj
from (select *
from v$lock
where type='TM'
and sid in (select sid
from v$lock
where block!=0)) l
, sys.obj$ o
, sys.user$ u
where o.obj# = l.ID1
and o.OWNER# = u.user#
/

prompt blocked sessions from V$LOCK

select /*+ ORDERED */
blocker.sid blocker_sid
, blocked.sid blocked_sid
, TRUNC(blocked.ctime/60) min_blocked
, blocked.request
from (select *
from v$lock
where block != 0
and type = 'TX') blocker
, v$lock blocked
where blocked.type='TXd blocked.block = 0
and blocked.id1 = blocker.id1
/

prompt blokers session details from V$SESSION

set lines 132
col username format a10 trunc
col osuser format a12 trunc
col machine format a15 trunc
col process format a15 trunc
col action format a50 trunc
SELECT sid
, serial#
, username
, osuser
, machine
FROM v$session
WHERE sid IN (select sid
from v$lock
where block != 0
and type = 'TX')
/