Distributed Computing System MCQ Questions and Answers

1. In distributed systems, a logical clock is associated with

Each instruction

Each process

Each register

None of the mentioned

In distributed systems, a logical clock is associated with each process. This is because in a distributed system, multiple processes are running concurrently and independently. Each process needs to have its own logical clock to maintain a consistent order of events and ensure synchronization among the processes. The logical clock helps in determining the relative ordering of events across different processes, even if there is no global clock available in the system. Therefore, associating a logical clock with each process is necessary in distributed systems.

Explanation

In distributed systems, a logical clock is associated with each process. This is because in a distributed system, multiple processes are running concurrently and independently. Each process needs to have its own logical clock to maintain a consistent order of events and ensure synchronization among the processes. The logical clock helps in determining the relative ordering of events across different processes, even if there is no global clock available in the system. Therefore, associating a logical clock with each process is necessary in distributed systems.

2. A process can enter into its critical section

Anytime

When it receives a reply message from its parent process

When it receives a reply message from all other processes in the system

None of the mentioned

In a distributed system, a process enters its critical section when it receives a reply message from all other processes in the system. This ensures that all other processes have completed their critical sections and are ready to proceed. By waiting for all processes to reply, it guarantees that there is no concurrent access to shared resources, preventing any conflicts or inconsistencies. This synchronization mechanism ensures the correct and orderly execution of critical sections in a distributed system.

Explanation

In a distributed system, a process enters its critical section when it receives a reply message from all other processes in the system. This ensures that all other processes have completed their critical sections and are ready to proceed. By waiting for all processes to reply, it guarantees that there is no concurrent access to shared resources, preventing any conflicts or inconsistencies. This synchronization mechanism ensures the correct and orderly execution of critical sections in a distributed system.

3. Event a has a Lamport timestamp of 4. Event b has a Lamport timestamp of 8. What can we tell about events a and b?

Events a and b are causally related.

Events a and b are concurrent

If events a and b are causally related, then event a happened before event b .

Event a happened before event b .

Based on the given information, we can conclude that events a and b are causally related. This is because event b has a higher Lamport timestamp than event a, indicating that event b occurred after event a. Therefore, we can infer that event a happened before event b.

Explanation

Based on the given information, we can conclude that events a and b are causally related. This is because event b has a higher Lamport timestamp than event a, indicating that event b occurred after event a. Therefore, we can infer that event a happened before event b.

4. In the token passing approach of distributed systems, processes are organized in a ring structure

Logically

Physically

Both logically and physically

None of the mentioned

In the token passing approach of distributed systems, processes are organized in a ring structure logically. This means that the processes are connected in a circular manner, where each process has a direct connection to its neighboring processes. The logical ring structure allows for the orderly passing of a token, which is used to control access to shared resources. Each process in the ring takes turns holding the token and can only access the shared resource when it possesses the token. This logical organization ensures that the token is passed in a predetermined order, preventing conflicts and ensuring fairness in resource allocation.

Explanation

In the token passing approach of distributed systems, processes are organized in a ring structure logically. This means that the processes are connected in a circular manner, where each process has a direct connection to its neighboring processes. The logical ring structure allows for the orderly passing of a token, which is used to control access to shared resources. Each process in the ring takes turns holding the token and can only access the shared resource when it possesses the token. This logical organization ensures that the token is passed in a predetermined order, preventing conflicts and ensuring fairness in resource allocation.

5. Which event is concurrent with the vector clock (2, 8, 4)?

(3, 9, 5)

(3, 8, 4)

(1, 7, 3)

(4, 8, 2)

The event (4, 8, 2) is concurrent with the vector clock (2, 8, 4) because all three components of the vector clock are less than or equal to the corresponding components of the event's vector clock. In other words, the event (4, 8, 2) could have happened at the same time or after the event represented by the vector clock (2, 8, 4).

Explanation

The event (4, 8, 2) is concurrent with the vector clock (2, 8, 4) because all three components of the vector clock are less than or equal to the corresponding components of the event's vector clock. In other words, the event (4, 8, 2) could have happened at the same time or after the event represented by the vector clock (2, 8, 4).

6. A bully election algorithm:

Picks the process with the largest ID.

Picks the first process to respond to an election request.

Relies on majority vote to pick the winning process.

Assigns the role of coordinator to the processs holding the token at the time of election.

A bully election algorithm picks the process with the largest ID as the coordinator. This means that in a system where multiple processes are competing to become the coordinator, the process with the highest ID is considered the most powerful and capable of handling the coordination responsibilities. By selecting the process with the largest ID, the algorithm ensures that the coordinator role is assigned to the most capable process in terms of its ID value.

Explanation

A bully election algorithm picks the process with the largest ID as the coordinator. This means that in a system where multiple processes are competing to become the coordinator, the process with the highest ID is considered the most powerful and capable of handling the coordination responsibilities. By selecting the process with the largest ID, the algorithm ensures that the coordinator role is assigned to the most capable process in terms of its ID value.

7. Which set of events is concurrent (all events are concurrent with each other)?

(3, 1, 5, 7), (3, 2, 6, 7), (2, 1, 6, 8)

(2, 1, 3, 4), (2, 2, 3, 3), (3, 3, 2, 5)

(1, 2, 3, 4), (2, 3, 4, 5), (3, 4, 5, 6)

(1, 5, 6, 7), (1, 4, 5, 7), (1, 3, 2, 2)

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Explanation

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8. The ring election algorithm works by:

Having all nodes in a ring of processors send a message to a coordinator who will elect the leader.

Sending a token around a set of nodes. Whoever has the token is the coordinator.

Sending a message around all available nodes and choosing the first one on the resultant list.

Building a list of all live nodes and choosing the largest numbered node in the list.

The ring election algorithm works by building a list of all live nodes and choosing the largest numbered node in the list. This means that each node in the ring sends a message to all other nodes to determine their availability. Then, the node with the highest number (assuming the nodes are numbered) is elected as the leader or coordinator. This approach ensures that the node with the highest number, which usually represents the highest priority, becomes the leader.

Explanation

The ring election algorithm works by building a list of all live nodes and choosing the largest numbered node in the list. This means that each node in the ring sends a message to all other nodes to determine their availability. Then, the node with the highest number (assuming the nodes are numbered) is elected as the leader or coordinator. This approach ensures that the node with the highest number, which usually represents the highest priority, becomes the leader.

9. Which mutual exclusion algorithm is useful when the membership of the group is unknown?

Centralized

Lamport’s.

Token ring

All of the above.

The centralized mutual exclusion algorithm is useful when the membership of the group is unknown because it allows for a single central entity to control access to a shared resource. In this algorithm, all requests for access to the resource are sent to the central entity, which then grants access to one request at a time. This approach is effective in situations where the group membership is unknown because it does not require knowledge of the other participants in the group.

Explanation

The centralized mutual exclusion algorithm is useful when the membership of the group is unknown because it allows for a single central entity to control access to a shared resource. In this algorithm, all requests for access to the resource are sent to the central entity, which then grants access to one request at a time. This approach is effective in situations where the group membership is unknown because it does not require knowledge of the other participants in the group.

10. The Ricart & Agrawala distributed mutual exclusion algorithm is

More efficient and more fault tolerant than a centralized algorithm.

Less efficient and less fault tolerant than a centralized algorithm

Less efficient but more fault tolerant than a centralized algorithm.

More efficient but less fault tolerant than a centralized algorithm.

The Ricart & Agrawala distributed mutual exclusion algorithm is less efficient and less fault tolerant than a centralized algorithm. This is because in a distributed algorithm, multiple processes need to communicate and coordinate with each other to achieve mutual exclusion, which introduces overhead and can lead to delays. Additionally, in a distributed system, there is a higher probability of failures and network partitions, which can further impact the algorithm's fault tolerance compared to a centralized algorithm.

Explanation

The Ricart & Agrawala distributed mutual exclusion algorithm is less efficient and less fault tolerant than a centralized algorithm. This is because in a distributed algorithm, multiple processes need to communicate and coordinate with each other to achieve mutual exclusion, which introduces overhead and can lead to delays. Additionally, in a distributed system, there is a higher probability of failures and network partitions, which can further impact the algorithm's fault tolerance compared to a centralized algorithm.