COMP212 Distributed Systems UPDATED
Exam Questions and CORRECT Answers
Distributed System - CORRECT ANSWER - Collection of independent computers that
appears to its users as a single coherent system
Main goals of a distributed System - CORRECT ANSWER - 1. Easy connection between
users/resources
2. Transparency
3. Openness
4. Reliability
5. Performance
6. Scalability
Transparent Distributed system - CORRECT ANSWER - A distributed system that appears
to its users as if it were only a single computer system
Scalable Distributed System - CORRECT ANSWER - One that is capable of growing in
size, the maximum distance between its participants (geographical), and the number of
administrative domains in it
Processors - CORRECT ANSWER - Computing entities.
Usually execute the same algorithm
Networks - CORRECT ANSWER - Connects processors.
EX. ring, tree, complete network
,Processors communicate by interchanging messages through the links of the network
What should happen in a round? - CORRECT ANSWER - 1. read incoming messages
2. Update states
3. Generate new messages, put them in transit
4. messages should be transmitted (Could also come first)
What are some distributed tasks/problems? - CORRECT ANSWER - Message sending,
leader election
Distributed algorithm - CORRECT ANSWER - 1. executed by all processors
2. May have some input (ids, other info)and have some initial state
3. Every processor reads incoming messages/updates states/generates out going messages
4. Network delivers the messages
5. Next round begins
6. Processors produce some output
Informal description (of an algorithm) - CORRECT ANSWER - Gives the main idea in
verbal form
Must be clear and concise to provide an accurate highlight/sketch of how the algorithm works
Psuedocode - CORRECT ANSWER - Informal code
A piece of code to be re-executed by all processors in every round
What should be taken into consideration when devising an algorithm? - CORRECT
ANSWER - 1. Convince that it is correct
2. Analyze its performance
, Correctness - CORRECT ANSWER - Proof that the algorithm does as expected
Performance - CORRECT ANSWER - Measured by 3 things:
1. Time Complexity
2. Space complexity
3. Communication Complexity
Time complexity - CORRECT ANSWER - measures the time it takes for an algorithm to
execute (ex # rounds required)
Space complexity - CORRECT ANSWER - A measurement of how much memory is used
by the processors during the runtime of the algorithms
Communication Complexity - CORRECT ANSWER - A measurement of message size
and quantities during the execution of an algorithm
How is a spanning tree of a network given? - CORRECT ANSWER - • Network G = (V,
E)
• Eʹ ⊆ E specifies a spanning tree T = (V, Eʹ)
• Root: u0 (leader)
• Processors know T in a distributed way
• Each u "i" knows: a parent "i", a set children
Time complexity of spanning tree broadcasting - CORRECT ANSWER - Depth d of T
Communication complexity of spanning tree broadcasting - CORRECT ANSWER -n-1
messages
Exam Questions and CORRECT Answers
Distributed System - CORRECT ANSWER - Collection of independent computers that
appears to its users as a single coherent system
Main goals of a distributed System - CORRECT ANSWER - 1. Easy connection between
users/resources
2. Transparency
3. Openness
4. Reliability
5. Performance
6. Scalability
Transparent Distributed system - CORRECT ANSWER - A distributed system that appears
to its users as if it were only a single computer system
Scalable Distributed System - CORRECT ANSWER - One that is capable of growing in
size, the maximum distance between its participants (geographical), and the number of
administrative domains in it
Processors - CORRECT ANSWER - Computing entities.
Usually execute the same algorithm
Networks - CORRECT ANSWER - Connects processors.
EX. ring, tree, complete network
,Processors communicate by interchanging messages through the links of the network
What should happen in a round? - CORRECT ANSWER - 1. read incoming messages
2. Update states
3. Generate new messages, put them in transit
4. messages should be transmitted (Could also come first)
What are some distributed tasks/problems? - CORRECT ANSWER - Message sending,
leader election
Distributed algorithm - CORRECT ANSWER - 1. executed by all processors
2. May have some input (ids, other info)and have some initial state
3. Every processor reads incoming messages/updates states/generates out going messages
4. Network delivers the messages
5. Next round begins
6. Processors produce some output
Informal description (of an algorithm) - CORRECT ANSWER - Gives the main idea in
verbal form
Must be clear and concise to provide an accurate highlight/sketch of how the algorithm works
Psuedocode - CORRECT ANSWER - Informal code
A piece of code to be re-executed by all processors in every round
What should be taken into consideration when devising an algorithm? - CORRECT
ANSWER - 1. Convince that it is correct
2. Analyze its performance
, Correctness - CORRECT ANSWER - Proof that the algorithm does as expected
Performance - CORRECT ANSWER - Measured by 3 things:
1. Time Complexity
2. Space complexity
3. Communication Complexity
Time complexity - CORRECT ANSWER - measures the time it takes for an algorithm to
execute (ex # rounds required)
Space complexity - CORRECT ANSWER - A measurement of how much memory is used
by the processors during the runtime of the algorithms
Communication Complexity - CORRECT ANSWER - A measurement of message size
and quantities during the execution of an algorithm
How is a spanning tree of a network given? - CORRECT ANSWER - • Network G = (V,
E)
• Eʹ ⊆ E specifies a spanning tree T = (V, Eʹ)
• Root: u0 (leader)
• Processors know T in a distributed way
• Each u "i" knows: a parent "i", a set children
Time complexity of spanning tree broadcasting - CORRECT ANSWER - Depth d of T
Communication complexity of spanning tree broadcasting - CORRECT ANSWER -n-1
messages
