Multiple choice Quiz

Question 1

q3. Which of these are abstractions that will be covered in the course?

Answer 1

Shared memory
Consensus
Reliable broadcast

Question 2

q3. Communication between components in our programming model can be done by:

Answer 2

Sending and receiving messages (only)

The event-based programming model can only communicate using events/messages, and doesn’t have shared variables.

Question 3

q3. Events in our model can be:

Answer 3

Messages
Timers
Conditions (e.g. x == 5 && y < 9)

Question 4

q3. The interface for a channel component have the following events:

Answer 4

A deliver indication event
A send request event
The events need to have the correct type (request or indication).

Question 5

q3. Which of the following should be part of a service specifications?

Answer 5

Service interface (API)
The required system model
Correctness properties

The specification only describes “what”, not “how”.

Question 6

q3. The service API describes

Answer 6

Responses (indication events)

Requests (request events)

Question 7

q3. A safety property states that

Answer 7

Nothing bad ever happens

Question 8

q3. A liveness property states that

Answer 8

Something good eventually happens

Question 9

q3. Is it the case that any property can be described as a conjunction of a safety property and a liveness property?

Answer 9

True

This has been proven formally

Question 10

q3. Safety can only be satisfied in infinite time

Safety can be violated in finite time

Answer 10

True

Question 11

q3. Liveness can only be violated in infinite time

Liveness can be satisfied in finite time

Answer 11

True

Question 12

q3. If it doesn’t fail in the (entire) execution

A correct process is one which never fails at any point in the execution.

Answer 12

True

Question 13

q3. In the crash-stop model, processes are not allowed to recover

Answer 13

True

Question 14

q3. In the crash-recovery model, a process is faulty if

Answer 14

It crashes and never recovers

It crashes and recovers infinitely often

Question 15

q3. Which of the following models are special cases of the crash-recovery model?

Answer 15

Omission

Crash-stop

Question 16

q3. The channel model…

Answer 16

Describes characteristics/guarantees of the network

Question 17

q3. When using a fair-loss link, if a message m is sent infinitely often by pi to pj, and neither crash, what is guaranteed to happen?

Answer 17

m is delivered an infinite number of times by pj

Question 18

q3. When using a fair-loss link, if a message m is sent 10 times by pi to pj, how many times may the message be delivered?

Answer 18

A message cannot be duplicated infinitely many times.

Question 19

q3. When using a fair-loss link, if a message m has not been sent by any process to pj, is pj allowed to deliver m?

Answer 19

No message is delivered unless it was sent.

Question 20

q3. When using stubborn links,if a node pi sends a message m to a correct node pj, and pi does not crash, how many times does pj deliver m?

Answer 20

An infinite number of times

Question 21

q3. Is it possible to implement the stubborn linkserviceusing the fair-loss link service?

Answer 21

True

Question 22

q3. When using perfect links, if a message m is sent by pi to pj, andneither pi nor pj crashes, is pj guaranteed to deliver m?

Answer 22

Yes, eventually (unbounded time)

Question 23

q3. When using perfect links, if a message m is sent by pi to pj, how many times is the message allowed to be delivered?

Answer 23

At most once

Question 24

q3. Which kind of system is described by the following statement: my server always processes requests within one week.

Answer 24

Synchronous system

There is a known bound on node processing delay.

Question 25

q3. Which kind of system is described by the following statement: my server processes requests within one week when it is running, and it will eventually be running for at least a week, I just don’t know when that will be.

Answer 25

Partially synchronous system

Question 26

q3. Safety in distributed systems describes:

Answer 26

a property that states that the system is robust to malicious behavior
a property that states that an event that is applicable is immediately applied
a property that holds for every execution in some configuration
a property that holds in every reachable configuration

Question 27

q3. Liveness in distributed systems describes:

Answer 27

a property that ensures low time complexity
a property that states that an event that is applicable infinitely many times is eventually applied
a property that holds for every execution in some configuration
a property that states that an event that is applicable infinitely many times is applied infinitely many times

Question 28

Select all cases when process p is correct, assuming the crash-recovery model. CORRECT

Answer 28

p crashes and recovers once every minute for the first year but after that never crashes again
p never crashes

Question 29

A new and highly advanced computer system has been installed and is running. The system guarantees that processes can send messages to each other in less than 10 microseconds. But the system needs to run an automatic tuning procedure before this 10 microsecond-guarantee starts to hold, and during this procedure the communication delays are unbounded. No one knows how long time the tuning procedure will take.
Which model best describes this system?

Answer 29

Partially synchronous