Rodrigo Albani de Campos gave a presentation on capacity planning at the São Paulo Perl Workshop. He discussed typical performance metrics like load average and CPU usage, but emphasized that time series data alone is not sufficient for capacity planning. He covered concepts like arrival rate, service time, and queues. De Campos demonstrated using the PDQ queuing model tool to model an Apache web server and explore "what if" scenarios. He provided several references for further reading on performance analysis and capacity planning techniques.

1. Capacity Planning
for fun & profit
beyond cacti and top
II São Paulo Perl Workshop
Rodrigo Albani de Campos - @xinu
camposr@gmail.com

2. Agenda
• Capacity planning primer: a tale of
discovery
• Metrics
• Queues
• Models

3. Why Perl ?
• Main reason: I feel comfortable with it
• Ubiquitous and free
• Plenty of stable statistics modules available
at CPAN
• Ultimately, it gets the job done

4. Capacity Planning
• Is just like sex...
• Everyone wants to do it
• Many say they’re doing it
• You always exaggerate how much of it
you’re doing
• Most people aren’t actually doing it (despite
their best efforts)
• Everybody else seems to be doing more
than you

5. A tale of discovery
There once was a system administrator...

6. A tale of discovery
How many ?
Actual capacity ?
Servers do we need ?
How much memory ?
What’s the predicted growth ?
IO Capacity ?

7. Typical Performance
Metrics
• Load Average - uptime
• The single most misunderstood metric
• CPU - mpstat
• IO - iostat
• Memory Usage - vmstat

8. Typical Performance
Metrics

9. Time series charts
I’m looking at you cacti huggers !
• Time series performance data is useful for:
• Troubleshooting
• Simplistic forecasting
• Find trends
• Identify seasonal behavior
• This left alone is NOT Capacity Planning

10. Frustration
• Computer systems can be harsh
• Most systems will not scale linearly
• Diminishing returns and lock contention
will punch you in the face
• “Oh but I’ve checked cacti and the CPU
was 25% idle”

11. Let’s put it in the Cloud
• We are moving back to an utility computing
model
• You’re charged per usage
• Even more important to care about
capacity planning !!!

12. Call the experts
• Cost per MIPS
• IBM System/370 model 158-3 - 1.0 MIPS @
1.0 MHz -1972
• Average purchase price: $ 771,000*
• No disks or peripherals included
• $ 4,082,039 by 2011
• Need to squeeze every drop of processing
power
* Source: http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3135.html

13. Queues
The not so typical performance metrics
• 1961 - CTSS was first
demonstrated at MIT
• 1965 - Allan Scherr used
machine repairman
problem to model a
time-shared system as
part of Project MAC
• Another offspring of
Project MAC is Multics

14. Queues
The not so typical performance metrics
Computer System
Disks
CPU

15. Queues
The not so typical performance metrics
(A) λ X (C)
S
Open/Closed W
Network R
A Arrival Count
λ Arrival Rate (A/T)
W Time spent in Queue
R Residence Time (W+S)
S Service Time
X System Throughput (C/T)
C Completed tasks count

16. Arrival Rate (λ)
• Pretty straightforward
• Requests per second/hour/day
• Not the same as throughput (X)
• Although in a steady state:
• A = C as T →∞
• λ=X

17. Service Time (S)
• Time spent in processing
• Web server response time
• Total query time
• IO operation time length

18. !"#$%&"'(%)"*+,'
Mythical Performance
!#)"
!#("
!#'"
• Not gonna happen...
!"#$%&"'(%)"'*+,'
!#&"
*+,-./+"0.1+234"
• Don’t believe vendor’s sales pitch
!#%"
• “In God we trust, all others must bring
data” - William Edwards Deming
!#$"
!"
!" (" $!" $(" %!" %(" &!" &(" '!" '("
-##%$./'0.1"'*2%1+3+,'

19. Mythical Performance
• Not gonna happen...
• Don’t believe vendor’s sales pitch
• “In God we trust, all others must bring
data” - William Edwards Deming

20. How to measure ?
• Apache: %D in mod_log_config
• nginx: $request_time in HttpLogModule
• use Benchmark;
• tcprstat - http://goo.gl/0cbYx
• collectd - http://goo.gl/OXKG7
• metrics - http://goo.gl/gQFVM
• sysstat - http://goo.gl/2aLul

21. How to measure ?
my ($date,$svctime) = (m/[(S+).+?s(d+)$/);
$arrivalRate{$date}++;
$serviceTimeAcc{$date} += $svctime;
[02/Jul/2010:14:00:18... 1863
Time to serve the
request,
in μseconds.

22. use Chart::Clicker;

23. use Chart::Clicker;

24. use Chart::Clicker;

25. use Chart::Clicker;
Average Hits/s = 65.142
Average Svc time = 0.0159

26. use Chart::Clicker;
Average Hits/s = 65.142
Average Svc time = 0.0159

27. What to look for ?
• Stretch factor
• Method/Operation
• Geolocation
• Cookies
• Use mod_logio to measure inbound
traffic as well

28. Modeling
Prediction is very difficult, especially if it’s about
the future.
Niels Bohr
Capacity planning is about setting expectations.
Even wrong expectations are better than no
expectations!
Neil J. Gunther - The Guerrilla Manifesto
http://goo.gl/lZKWH

29. Modeling
• A model is an abstraction of a complex
system
• A model allows us to observe phenomena
that cannot be easily replicated

30. Modeling Methods
• Statistics / Trending / Forecasting
• Pros:
• Easy to understand
• Tools readily available
• Cons:
• Hard to create “What-if” scenarios
• Hard to predict contention and
bottlenecks

31. Modeling Methods
• Queuing Analisys
• Pros:
• Allows you to make predictions when no
production data is available
• Allows you to create “What-if” scenarios
• Cons:
• Sometimes it can be unintuitive
• The math behind it can be difficult

32. Queues as models
Typical LAMP Stack
Clients
Requests Replies
Apache Application Database

33. Queues as models
What if ?
Clients
Requests Replies
Cache Apache Application Database

34. Queues as models
What happens if we use a 15k RPM disk ?
CPU Disk 10k
RPM

35. Queues as models
m1.small ? m1.large ? m1.xlarge ?
Virtual Cores X
EC2 CU
Memory Bus

36. use pdq;
• Available at http://goo.gl/s98wQ (not on
CPAN)
• PDQ is a queuing circuit solver by Neil J.
Gunther
• There’s a whole book about it
http://goo.gl/9MA2c

37. use pdq;
CreateNode() Define a queuing center
Define a traffic stream of an
CreateOpen()
open circuit
Define a traffic stream of a
CreateClosed()
closed circuit
Define the service demand for
SetDemand()
each of the queuing centers

38. use pdq;
Node Types
CEN Queuing Center
DLY Delay Center

39. use pdq;
Service Disciplines
FCFS First-come first-served
LCFS Last-come first-served
ISRV Infinite Server
PSHR Processor Sharing

40. use pdq;
• Apache Web Server
• Average Network RTD: 0.00921 seconds
• Added as a delay center in the circuit
• Average Arrival Rate: 65.142 hits/s
• Average Service time: 0.0159 seconds
• 128 worker threads

41. use pdq;
$workload = "httpd";
$httpMaxClient = 128;
pdq::Init("web server");
$arrivalRate = 65.142;
$serviceTime = 0.1159;
$pdq::streams =
pdq::CreateOpen($workload,
$arrivalRate);

42. pdq::Report();
Metric Value Unit
------ ----- ----
Workload: "httpd"
Number in system 8.0279 Trans
Mean throughput 65.1420 Trans/Sec
Response time 0.1232 Sec
Stretch factor 1.0626

43. pdq::Report();
Bounds Analysis:
Max throughput 1104.4003 Trans/Sec
Min response 0.1160 Sec

44. pdq::Report();
• Average request size: 145 KBytes
• ~ 1160 Kbits
• @1104 transactions / second:
• 1,280,640 Kbits /s ~ 1.28 Gbps

45. Resources and
References
• CMG Public Proceedings:
http://www.cmg.org/proceedings/
• Measure IT:
http://www.cmg.org/measureit/
• Guerrilla Capacity Planning
http://www.perfdynamics.com/Classes/
Outlines/guerilla.html

46. Resources and
References
• Performance by Design - Menasce, Dowdy,
Almeida - http://amzn.to/mpqfVO
• Capacity Planning for Web Performance:
Metrics, Models, and Methods - Daniel
Menasce,Virgilio Almeida - http://amzn.to/
lOATba
• Capacity Planning for Web Services: Metrics,
Models, and Methods - Daniel Menasce,
Virgilio Almeida - http://amzn.to/iClpsB

47. Resources and
References
• Guerrilla Capacity Planning: A Tactical
Approach to Planning for Highly Scalable
Applications and Services - Neil Gunther -
http://amzn.to/kfrfLK
• The Art of Computer Systems Performance
Analysis: Techniques for Experimental Design,
Measurement, Simulation, and Modeling - R.
K. Jain - http://amzn.to/jqud1I

48. Any questions ?