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Final Exam 2010
• Problem 3‐ Software Execution Model (36 marks)
ABC airlines maintains a Web site that provides static content with information about the company, along with dynamic functions. All users are allowed to:
• Check the status of today’s flights
• Request information on flight schedules, fares, and availability • Purchase tickets
Members of Frequent Flyer Club (Elite) are able to:
• Get current information about the status of their account (number of miles flown to date this year, number of miles available for award travel, most recent flights taken)
• Purchase tickets for multiple trips using either frequent flyer miles or a credit card
In order to ensure privacy and prevent unauthorized use of frequent flyer miles, access to frequent flyer accounts will require that the Elite member login by entering an account number and a personal identification number (PIN). When Elite members login, they will see a custom home page tailored to the preferences entered on their Member Profile form (e.g., showing specials on travel to Vancouver) and their flying habits (e.g., most frequent flight segments) as stored in the member history database. Members may update their Member Profiles online.
The on‐line system consists of several components displayed in the physical UML diagram as shown in Figure 1. The static pages are stored in the web server. The dynamic functions are executed in the application server. The member history and ticket information are stored in the database server. 1
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Figure 1: Component Diagram of the ABC Airline On-Line System
Use Case Diagram
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Sequence Diagram – Purchase ticket
Sequence Diagram –
getFlightPlanningPage
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Basic Execution Graph Notation
SOFT 437 – Course Review
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Sequence Diagram – Purchase ticket
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Software Execution Model Representation
SOFT 437
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Example 6‐2
Arrival rate, λ
Mean service time, S
0.4 jobs per sec
2 sec
We then calculate the following average values:
Throughput, X = λ
Utilization, U = XS
S
RT 
Residence time, 1U
Queue length, N = X * RT
SOFT 437 – Course Review
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Utilization on Multiple Resources
• Utilization of single resources
U=X * S
Utilization of multiple resources
Ui = U/m
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Service Demand Law
• The service demand on a device i
Di Vi Si
Ui
Di 
X0
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• Problem 4
A Web server has one CPU and one disk. It receives two types of HTTP requests: for small text files and for image files. The average arrival rates are 5 requests/sec for text files and 2 requests/sec for image files. The service times for the CPU and the disk are given below.
Arrival Rate (tps)
Service Demands (sec)
CPU
Disk
Utilizations (%)
CPU
Disk
Residence Time (sec)
CPU
Disk
Response Time
Average number of requests
Text
request
Image Request
5
2
0.1
0.08
0.1
0.15
SOFT 437 – Chapter 6
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Arrival Rate (tps)
Service Demands (sec)
CPU
Disk
Utilizations (%)
CPU
Disk
Residence Time (sec)
CPU
Disk
Response Time
Average number of requests
Text
request
5
Image Request
0.1
0.08
0.1
0.15
50
40
20
30
2
0.3
0.27
0.57
2.87
SOFT 437 – Chapter 6
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Problem 6 – Capacity Planning
(12 marks)
Consider a three-tier site, which consists of a web server, an application server and a
database server. The CPU service demand for the application server is 268.3 msec. Table 1
lists the processing speedups and the forecasted number of the transactions for the web site
for the next 3 years. At the beginning of year 2, a new algorithm is used to improve the
performance of the processing in the application server. The service demand is reduced to
26% of the service demand in year 1 if the new algorithm is use.
Year
1
2
3
Processing Speedup
1.00
1.60
2.56
Volume of Transactions (tps)
14
19
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Table 1: CPU Processing Speedup and Transaction Growth Assumptions
1) Show the CPU demands for the application server vary from year 1 to year 3
(6 marks)
1) What is the required number of the CPUs to reduce the utilization to an average of
50% over all CPUs in the application server in year 1?
(6 marks)
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Problem 7 – Performance Principles, Patterns and Anti-patterns (26 marks)
1) Describe the follow concepts and give an example on each concept
 Design Pattern
 Performance Pattern
 Software Anti-pattern
 Performance Anti-pattern
 Refactoring
(10
marks)
1) Describe the four independence principles
marks)
 Centering
 Fixing-point
 Locality
 Processing versus frequency
(8
1) Compare the following two solutions from the point of view of the independent performance principles. Which
solution is better - why?
(8 marks)
Solution 1: Write a transformation program that reads the storage structure of tool A and replaces certain
elements by the corresponding elements required by the storage structure of tool B. Intermediate
structures are used to keep the temporary result of the transformations. The intermediate structures
are stored in a temporary file.
Solution 2: Use a transformation generator that requires the following input: the grammar of the format
required by tool A, the grammar of the format required by tool B, transformation rules between the
grammars. The generator generates the software that constructs a tree structure from the input file,
transforms it into the corresponding tree structure of the output file and produces the output file. The
input file follows the grammar of tool A, the output file follows the grammar of tool B, and the
transformation is done using the input transformation rules.
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1) www.travel.com is an Internet-based travel agency. It has localized sites for 15 countries outside US. It books airline
tickets, hotel reservations, car rental, cruises, vacation packages, and various attractions. It also recommends related
services when a user selects a trip. For example, hotel information and car rental companies in the destination are
automatically listed in the web page once the flight tickets are selected. Figure 2 shows a screenshot of the home page of
www.travel.ca web site localized to the users from Canada.
Here is the list of the performance independence principles:
 centering
 fixing-point
 locality
 processing vs. frequency
Explain how the performance independence principles are applied in the design of the web site.
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