Oracle 10g Performance: chapter 02 aas

Average Active Sessions
(AAS)
The Golden Metric ?

Kyle Hailey
http://perfvision.com

#.1

In this Session
1. AAS
 Single Metric
 Shows DB Performance
 Two methods to calculate
 Sampling
 Time statistics
1. Yardstick
 Max CPU
 CPU Count
 To measure AAS against
1. Subcomponents
 CPU
 Waits
 Time series

02/20/13 Copyright 2006 Kyle Hailey #.2
2

Database Performance
How quick can you find
 Bottleneck in DB
 If DB is idle
 Current DB Load
 what is DB Load ? what the *!####!
 What do you use? *!*? is the
 Statspack/AWR
database
 V$active_session_history
 Alerts
doing ?!
 what do you alert on ?

02/20/13 #.3
3

Active Session
Database Machine
SGA Shadow
Shadow
Process Process

Shadow
Shadow Shadow
Process
Process Process

SQL* SQL*
Plus Plus
Application

Copyright 2006 Kyle Hailey #.4

Active Session
Shadow
Process
Database (shadow process)

idle Query 1 idle Query 2 idle Query 3 idle

Active Active Active
Time

Typing waiting typing waiting typing waiting Have a coffee

SQL*Plus (ie application)


Active Session
Database
User 1
User 2
User 3
User 4

=
4 Active Sessions
3
2
1

Graph represents # of sessions active, but also represents
amount of time active in the database

#.6

Active Session

4 Active Sessions
3
2
1

For Every Active Session there is a user (or application) waiting

1
2
3
4 Users Waiting


Measuring Active Sessions

Sampling Every Second

...

User 1

User 2

User 3

If happens a lot or for long … we’ll catch it, guaranteed

Fast query run often

Fast query run rarely

Slow query


Sampling is like taking Pictures


Active Session
Database

To execute a query , some CPU will be used but we also might spend time
waiting for IO or on waiting for concurrency resources like latches

Database

CPU IO Wait
Activity can thus further be broken down into the type of activity: CPU, IO or WAIT

Latency
Work Contention

Graphical ASH

Session 1

Session 2

Session 3

Session 4

TIME

#.11

Graph of User States


One Second Graph


15 Second Averages


Maximum CPU Line


Idle Users


OEM Perf Page


AAS in OEM

AAS

LOAD

#.18

The Power ASH gives AAS
DB Home

Performance

Based on TIME AAS=db
(events Statistics) time/elapsed time

Top Activity

AAS=count active
Based on
users /samples
ASH


DB TIME = area under the curve

Height = # of Sessions
Width = seconds
Area under curve = DB Time

n
DB Time = active sessions(ti) * Δt

DB Time = sum of active time in database

AAS Sources
AAS = DB Time/Elapsed Time
1. Manually from
 v$sysstat (9i : v$system_event )
1. Statspack
 Need several calculations
1. AWR
 One calculation
1. OEM 10g
 Directly displayed

21

1. Manually
AAS = DB TIME / Elapsed Time
DB Time (DBT) = Time Spent in Database
DB TIME (10g) = select value from v$sysstat
select value from v$sysstat
where name = ‘DB time’
where name = ‘DB time’;
‘DB time’;

DB TIME (9i) = Select sum(time_waited) from v$system_event
Select sum(time_waited) from v$system_event
where event not in (( ... idle events …);
where event not in ... idle events …);
+
+
Select value from v$sysstat
Select value from v$sysstat
where name = ‘CPU used by this session’;
where name = ‘CPU used by this session’;
still need to take delta values
Note: stats$idle_event : 70
v$event_name.wait_class=‘Idle’ :62

2. Statspack AAS
Look for
Elapsed Time
Top 5 Timed Events
 Start at line 52 of about 1300

23

2. Statspack AAS
 Elapsed Time
STATSPACK report for
STATSPACK report for

LABSF03 1420044432
LABSF03 1420044432 labsf03
labsf03 1 10.1.0.2.0 NO labsfr
1 10.1.0.2.0 NO labsfr
Snap Id
Snap Id Snap Time
Snap Time Sessions Curs/Sess
Sessions Curs/Sess
Begin Snap:
Begin Snap: 1 03-Apr-06 12:34:06
1 03-Apr-06 12:34:06 18
18 5.6
5.6
End Snap:
End Snap: 2 03-Apr-06 12:34:36
2 03-Apr-06 12:34:36 18
18 4.8
4.8
Elapsed:
Elapsed: 1.00 (mins)
1.00 (mins)

 Look at Top 5 Timed Events
Top 5 Timed Events
Top 5 Timed Events
~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~ % Total
% Total
Event
Event Waits
Waits Time (s)
Time (s) Call Time
Call Time
buffer busy waits
buffer busy waits 2,748
2,748 250
250 78.72
78.72
CPU time
CPU time 32
32 10.16
10.16
free buffer waits
free buffer waits 1,588
1,588 15
15 4.63
4.63
write complete waits
write complete waits 10
10 88 2.51
2.51
log buffer space
log buffer space 306
306 55 1.51
1.51

24

2. Statspack AAS
Top 5 Timed Events
Top 5 Timed Events

Event Time (s)
 DBTIME= CPU + WAITS Event
-----------------
Time (s)
----------------- -----
-----
 CPU = 32 buffer busy waits
buffer busy waits 250
250
CPU time
CPU time 32
32
 WAITS = 250+15+8+5 = 278 secs free buffer waits 15
free buffer waits 15
DBTIME=320 write complete waits
write complete waits 88
log buffer space 5
 Elapsed Time = 60 secs log buffer space 5

 320 secs / 60 secs
AAS = 5.1

25

3. AWR Report
AAS = DB Time/Elapsed Time

23.56/59.66 = 0.39

AAS= 0.39

02/20/13 #.26
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4. OEM 10g
•OEM 10g

AAS = ~0.75

02/20/13 #.27
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Got AAS, Now What ?
We Need one more item:

CPU Count

 # of CPUs available on System
 Shared with other applications
 Need to track CPU used on the system as well
 On dual & quad cores, lower the CPU count
 Represents max active sessions that can do work

28

CPU Count
 # of CPUs available in
 Statspack 10g
 AWR report
 OEM 10g

 Statspack 9i # of CPUs missing # of CPUs
SQLPLUS> show parameters cpu_count
SQLPLUS> show parameters cpu_count

NAME
NAME VALUE
VALUE
------------------ ----------
------------------ ----------
cpu_count
cpu_count 22

29

What’s the DB Doing?!

It’s 2am … your manager calls

Whip out the stethoscope:
AAS
what the *!####!*!
*? is the database
doing ?!
30

AAS Formulas
Use CPU count as yardstick:

 AAS < 1 Ideal world –
Database is not blocked one database
 AAS ~= 0 solution
Database basically idle
Problems are in the APP not DB
track CPU at OS
 AAS < # of CPUs
CPU available
Are any single sessions 100% active?
AAS > 1
 AAS > # of CPUs still want to know
Could have performance problems if a single user is
 AAS >> # of CPUS 100% active
There is a bottleneck

31

Available CPU vs AAS
Statspack
 DBTIME= CPU + WAITS AAS = 5.1
AAS = 5.1 AAS far above
 CPU = 32
 WAITS = 250+15+8+5 = 278 secs available CPU

DBTIME=320
Elapsed Time = 60 secs
# of CPU = 2
# of CPU = 2 => problem
 320 secs / 60 secs
AAS = 5.1

AWR Report AAS = 0.39
AAS = 0.39
# of CPU = 2
# of CPU = 2
AAS < 1 , database is fine

AAS = 0.75
AAS = 0.75
# of CPU = 2
# of CPU = 2
AAS < 1 , database is fine
32

Going Farther with AAS
 AAS can tell you a lot
 But it’s components tell you much more
 To go farther need the components of AAS
1. CPU
2. Wait
3. Value over time
 Only OEM 10g shows the value over time, Statspack and AWR
are aggregated over the snapshot period

33

EM DB Home Page


OEM 10g Perf Pages
DB Home

AAS Point in Time

Performance

AAS over Time


AAS Components : OEM 10g

OEM 10g
Performance Page

Real CPU available:
Max CPU - non instance CPU
Available CPU AAS:
CPU + WAIT

02/20/13 #.36
36

OEM 10g

Looks
Relax Get to Work! OK
But …
02/20/13 #.37
37

Idle Database – Perf Page
 Value of proving the database is
Idle
 It’s the Databases Fault
 How many times do you hear that?
 Database Idle
 No load on database
 Database “performance” is fine
 Under utilized
 Problem lies elsewhere
 Saved me time and stress many
times
 And weeks of debate about where the
problem is coming from


More than AAS and #CPU
Knowing your DB Profile


When to Tune
1. Machine
a) CPU
 Response times skewed
 100% CPU might be fine
 Users wait in queue (run queue) => machine
underpowered
a) Memory
 Paging
 Wait times skewed (ex : latch free)
 Erratic response times ( ex : ls )

1. Oracle Host CPU
Memory

1) Waits > CPU ? Oracle Load
(AAS)
 tune waits AAS >
#CPU
1) CPU > 100% ? Waits > CPU >
CPU
 tune top CPU SQL AAS > 1
Top Session
Waits
Top Wait Top SQL
1) Else
 It’s the application
Object Detail SQL Detail Wait Detail Session Detail File Detail

#.40
Copyright 2006 Kyle Hailey

Limited Analysis
 What if you find a problem ?
Of the 800 waits which in order to solve most need to know
What SQL
Which sessions
Values of P1, P2 and P3
Statspack and AWR fail

AAS = DB TIME / Elapsed Time

But there is another way …
02/20/13 #.41
41

AAS based on ASH
 ASH - Active Session History
 v$active_session_history
 Samples sessions once a second
 AAS = count(*) / elapsed_seconds
A statistical approximation, but surprisingly close
 ASH data source empowers drilldowns
 Top Sql
 Top Waits
 Details p1,p2,p3 and more

42

ASH
vs
Statistics

 Statistics
 are more expensive
 have lag time
 lack clear identification of culprits


Statistic Lag Time
Samples (ASH)

Slight Lags

Statistics


CPU Lag Problem
 ASH is the only way to see CPU usage realtime
 V$sysstat reports CPU but
 isonly updated at the end of the call.
 Long calls look deceiving like no CPU is being used

 Time Model also reports CPU
 Updated quicker


CPU in ASH vs Stats


2. OEM 10g : Top Activity
•Top Activity
•Based on ASH
•Enables Drilldowns
•Top SQL
•Top Session
•Drill into a session
• Stats
• Raw waits
• Open cursors
• General info
•Drill into a SQL
• Stats and text
• Users executing
• Explain plan
• Tuning options

02/20/13 #.47
47

Top Activity : Based on ASH

missing

Thanks
To
ASH


AAS – %Session Time Issue

Whenever AAS > 1
I want to know if any
one session is 100% active
Unfortunately OEM isn’t set up for this
(ASHMON, my free tool, is )


Top Activity: ASH Sessions

Many Users Active

On Performance Page, no way to tell how many users


Top Activity: ASH Sessions

Two Users Active

Shown in % DB Time
Missing % Session Time


OEM 10g Perf Pages
DB Home
Top Activity

Performance

Top Activity
SQL
Session
SQL
Session


Session : ASH Activity


SQL : ASH Activity


AAS from ASH
1. ASHRPT
 Based entirely on
v$active_session_history
 @?/rdbms/admin/ashrpt.sql
 Exec ASH_REPORT_TEXT/HTML

select * from table
(dbms_workload_repository.ash_report_text(
(select dbid from v$database),
1,
sysdate – 1/24,
sysdate )) ;

55

1. ASHRPT
ASH Report For TESTDB/testdb
ASH Report For TESTDB/testdb
DB Name DB Id Instance Inst Num Release RAC Host
DB Name DB Id Instance Inst Num Release RAC Host
TESTDB 2371570538 testdb 11 10.2.0.1.0 NO sdbe604a
TESTDB 2371570538 testdb 10.2.0.1.0 NO sdbe604a
CPUs SGA Size Buffer Cache Shared Pool ASH Buffer Size
CPUs SGA Size Buffer Cache Shared Pool ASH Buffer Size
22 1,000M (100%) 468M (46.8%) 112M (11.2%) 4.0M (0.4%)
1,000M (100%) 468M (46.8%) 112M (11.2%) 4.0M (0.4%)
Analysis Begin Time: 21-Apr-06 12:00:01
Analysis Begin Time: 21-Apr-06 12:00:01
Analysis End Time: 21-Apr-06 12:05:01
Analysis End Time: 21-Apr-06 12:05:01
Elapsed Time: 5.0 (mins)
Elapsed Time: 5.0 (mins)
Sample Count: 3,716
Sample Count: 3,716
Average Active Sessions: 12.39
Average Active Sessions: 12.39
Avg. Active Session per CPU: 6.19
Avg. Active Session per CPU: 6.19
Report Target: None specified
Report Target: None specified
Top User Events DB/Inst: TESTDB/testdb (Apr 21 12:00 to 12:05)
Top User Events DB/Inst: TESTDB/testdb (Apr 21 12:00 to 12:05)
Avg Active
Avg Active
Event Event Class %% Activity
Event Event Class Activity Sessions
Sessions
CPU ++ Wait for CPU CPU 67.98 8.42
CPU Wait for CPU CPU 67.98 8.42
enq: TX -- row lock contention Application 23.98 2.97
enq: TX row lock contention Application 23.98 2.97
buffer busy waits Concurrency 4.66 0.58
buffer busy waits Concurrency 4.66 0.58
latch: cache buffers chains Concurrency 2.26 0.28
latch: cache buffers chains Concurrency 2.26 0.28

56

1. ASH RPT

1) General info
1) General info 9) Top SQL using literals
9) Top SQL using literals
2) Top User Events ***
2) Top User Events *** 10) Top Sessions ***
10) Top Sessions ***
3) Top Background Events
3) Top Background Events 11) Top Blocking Sessions
11) Top Blocking Sessions
4) Top Event P1/P2/P3 Values
4) Top Event P1/P2/P3 Values 12) Top Sessions running PQs
12) Top Sessions running PQs
5) Top Service/Module
5) Top Service/Module 13) Top DB Objects
13) Top DB Objects
6) Top Client IDs
6) Top Client IDs 14) Top DB Files
14) Top DB Files
7) Top SQL Command Types
7) Top SQL Command Types 15) Top Latches
15) Top Latches
8) Top SQL Statements ***
8) Top SQL Statements *** 16) Activity Over Time ***
16) Activity Over Time ***

57

1. ASHRPT over Time

Waits over Time
 Not in AAS

Difficult but better
than nothing

Compare to …
02/20/13 #.58
58

3. Custom Scripts
Hate Graphics ?
 Query v$active_session_history directly
 Join to dba_hist_active_sess_history for week of data

act.sql
 Like top 5 timed events
Aveact.sql
 Charts with text AAS by hour (15 minute, minute , etc)
Aveactn.sql
 Ditto,
with top 2 wait events per bucket
Following Scripts Available on
 http://perfvision.com/ashscripts.php

02/20/13 #.59
59

3. Custom Scripts
@act
@act
Analysis Begin Time :
Analysis Begin Time : 2007-07-24 11:04:48
2007-07-24 11:04:48
Analysis End
Analysis End Time :
Time : 2007-07-24 11:19:45
2007-07-24 11:19:45
Start time, mins ago:
Start time, mins ago: 15
15
Request Duration
Request Duration :: 15
15
Collections
Collections :: 528
528
Data Values
Data Values :: 3327
3327
Elapsed Time: 15 mins
Elapsed Time: 15 mins
WAIT_EVENT
WAIT_EVENT CNT
CNT % Active Ave_Act_Sess
% Active Ave_Act_Sess
latch free
latch free 10
10 .3
.3 .02
.02
log buffer space
log buffer space 13
13 .39
.39 .02
.02
buffer busy waits
buffer busy waits 14
14 .42
.42 .03
.03
db file scattered read
db file scattered read 15
15 .45
.45 .03
.03
library cache pin
library cache pin 78
78 2.34
2.34 .15
.15
log file sync
log file sync 213
213 6.40
6.40 .40
.40
ON CPU
ON CPU 726
726 21.82
21.82 1.38
1.38
enqueue
enqueue 855
855 25.70
25.70 1.62
1.62
db file sequential read
db file sequential read 1399
1399 42.05
42.05 2.65
2.65
sum
sum 6.30
6.30

60

3. Custom Scripts
@aveact
@aveact
TM
TM NPTS AVEACT GRAPH
NPTS AVEACT GRAPH CPU WAITS
CPU WAITS
---------------- ------ ------- ---------------------- ---- -----
---------------- ------ ------- ---------------------- ---- -----
06-AUG 13:00:00
06-AUG 13:00:00 270
270 .33 +-
.33 +- 22 29
29 59
59
06-AUG 14:00:00
06-AUG 14:00:00 1040
1040 2.24 ++--------2---
2.24 ++--------2--- 341 1984
341 1984
06-AUG 15:00:00
06-AUG 15:00:00 623
623 6.67 ++++------2----------
6.67 ++++------2---------- 438 3718
438 3718
06-AUG 16:00:00
06-AUG 16:00:00 1088
1088 2.59 ++--------2----
2.59 ++--------2---- 335 2486
335 2486
06-AUG 17:00:00
06-AUG 17:00:00 1104
1104 1.26 ++-----
1.26 ++----- 22 349 1043
349 1043
06-AUG 18:00:00
06-AUG 18:00:00 1093
1093 1.38 +++----
1.38 +++---- 22 663
663 842
842
06-AUG 19:00:00
06-AUG 19:00:00 1012
1012 1.74 ++------- 2
1.74 ++------- 2 373 1388
373 1388
06-AUG 20:00:00
06-AUG 20:00:00 1131
1131 .99 +----
.99 +---- 22 304
304 820
820
06-AUG 21:00:00
06-AUG 21:00:00 1111
1111 1.22 ++-----
1.22 ++----- 22 344 1012
344 1012
06-AUG 22:00:00
06-AUG 22:00:00 1010
1010 1.66 ++------ 2
1.66 ++------ 2 414 1259
414 1259
06-AUG 23:00:00
06-AUG 23:00:00 1120
1120 1.08 +----
1.08 +---- 22 298
298 913
913
07-AUG 00:00:00
07-AUG 00:00:00 1024
1024 .83 +---
.83 +--- 22 273
273 576
576
07-AUG 01:00:00
07-AUG 01:00:00 1006
1006 1.74 ++------- 2
1.74 ++------- 2 319 1428
319 1428
07-AUG 02:00:00
07-AUG 02:00:00 1090
1090 2.47 ++--------2----
2.47 ++--------2---- 347 2345
347 2345
07-AUG 03:00:00
07-AUG 03:00:00 687
687 6.59 +++-------2----------
6.59 +++-------2---------- 382 4142
382 4142
07-AUG 04:00:00
07-AUG 04:00:00 1004
1004 1.95 ++++++--- 2
1.95 ++++++--- 2 1299
1299 659
659
07-AUG 05:00:00
07-AUG 05:00:00 1104
1104 3.08 +++++-----2------
3.08 +++++-----2------ 1170 2226
1170 2226
07-AUG 06:00:00
07-AUG 06:00:00 1122
1122 1.91 +++++++-- 2
1.91 +++++++-- 2 1582
1582 558
558

61

Aveact.sql


Aveact.sql

“-” = WAIT
“+” = CPU
which waits ? -> aveactn.sql

Aveactn.sql


Summary
 AAS: Two Sources Host CPU
Memory

1. v$system_event & v$sysstat Oracle Load
(AAS)
 Performance page in OEM
 Statspack, awr report AAS >
 Indirect – based on time converted to AAS #CPU
 Accurate
 Lags (especially CPU) AAS > Waits > CPU >
1 CPU Waits
 Limits analysis
Top Session Top Wait Top SQL
1. v$active_session_history
 Top activity in OEM
 ashrpt
 Direct measure of AAS Object Detail SQL Detail Wait Detail Session Detail File Detail
 Real time
 Approximation
 ***Allows drilldowns***
SQL Tuning
 Tuning: ADDM Advisor
 Machine first – CPU, Memory
 Oracle
 AAS ~= 0 Idle
 AAS > 1 : possible sessions blocked
 AAS > # CPU : bottleneck

65

Q1

What is the easiest way to find the load on the database
b. Average Active Sessions takes into
account all the major criteria in Oracle
a. top 5 timed eventsperformance - cpu usage, wait time, elapsed
time
b. Average Active Sessions and CPU count
others:
c. The transaction rate
d. The commit rate a. lacks the elapsed time
c & d - the amount of load created by
commits and transactions varies drastically
between database to database and even
between different loads on a database during
the day


Q2

Average active sessions, the measurement in the
performance chart in OEM 10g can be calculated by which
formula(s)
a. db time / elapsed time
b. wait time / elapsed time
answer
c. count of rows in v$active_session_history over an
a,c,d
interval/ number of samples in interval
c, d are equivalent because ASH samples
d. count of rows in v$active_session_history / seconds of
once a second
elapsed time
others
b doesn't work because it is missing CPU
time


Q3

If Average Active Session is less than one, we can say
a. the database is using less than 100% CPU on machine
b. the database is using 100% CPU
c. No session is completely blocked
d. Database performance should be acceptable

answer
a, c and d


Q4

An Average Active Session value of zero
means
a. the database is down
b. the database is hung
c. the database is idle
d. the database is overloaded

answer
c


Q5

CPU is updated in v$sysstat
a. when call finishes
b. every second
c. every five seconds
d. in real time
a - which can be a problem in
monitoring tools if the call last a long
time showing no CPU usage until the
call finishes, then reporting an
unrealistic spike of CPU when the
call finishes


Oracle 10g Performance: chapter 02 aas

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