2900649
Questão 1
Questão
Which of the following is false about the Repulsion forces approach in large scale coordinator election
Responda
-
each token is “repulsed” by nearby tokens (token holder sends token to another peer if too many tokens nearby)
-
token must be held by a node for a set time period before node can become superpeer
-
each node holding a token learns about other tokenholders
-
a superpeer which receives another token sends it to the lowest prime numbered neighbour
Questão 2
Questão
How can a coordinator failure be addressed in a centralised mutual exclusion system?
Responda
-
By using election algorithms to change the coordinator
-
By using triple modular redundancy to compare the results of two coordinators
-
By emitting a heartbeat that informs other nodes when the coordinator cannot provide a lock
-
By moving the coordinator periodically to the next node in the token ring
Questão 3
Questão
Which of these is not a drawback of a typical distributed mutual exclusion algorithm?
Responda
-
large number of messages required
-
one slow process slows down others
-
more points of failure
-
locks may be granted unfairly
Questão 4
Questão
Which of the following is true about Lamport's algorithm
Responda
-
when a message is received, its time is compared against the local clock. If the local clock is less than C(b), it is set to C(b) + 1
-
messages carry their sending time according to the receiver's clock e.g., C(b)
-
between any two events, the clock must tick at least twice (i.e. one on the transmitting side, one on the receiving side)
-
Events occurring in processes that do not interact (even indirectly through third parties) are said to be concurrent
Questão 5
Questão
In the bully algorithm with nodes 1,2,3,4,5,6,7 if 7 is the coordinator and 4 notices the coordinator has crashed, who will be the new coordinator?
Responda
-
6
-
4
-
1
-
7 after it reboots
Questão 6
Questão
Which of the following is false about wireless network clock synchronisation algorithms
Responda
-
Clock synchronisation is difficult because nodes cannot always contact one another
-
Nodes are resource-constrained
-
Receivers record difference between reference message timestamp and their own clock
-
The coordinating node must transmit at a higher power level to ensure all nodes can receive clock broadcasts
Questão 7
Questão
Which of the following is false about Lamport's algorithm?
Responda
-
if a and b are events in the same process, and a occurs before b, then a - > b is true
-
if a is the event of a message being sent by one process, and b is the receipt of that message in another process, then a ->b is also true
-
a -> b and b -> c, then a -> c
-
if a is the event of a message being sent by one process, and b is the receipt of that message in another process, then b -> a is also true
Questão 8
Questão
Which of these are clock synchronisation protocols
Responda
-
Network Time Protocol, The Berkeley Algorithm
-
Network Time Protocol, Town Clock Algorithm, The Berkeley Algorithm
-
UTC lock algorithm, NTP
-
Network Time Protocol, Town Clock Algorithm
Questão 9
Questão
Which is true about NTP?
Responda
-
Stands for Numerical Time Protocol
-
Daemon calculates new time based on average of reported values
-
In general, synchronising with stratum-k server makes you stratum-k+1
-
Stratum-1 servers typically have direct access to a reference clock
Questão 10
Questão
What issue is addressed by a vector clock?
Responda
-
Lamport’s algorithm does not capture causality
-
Sometimes messages are received out of order
-
Sometimes messages are created at precisely the same time
-
Sometimes events must be recorded before an event which occurred after it
Questão 11
Questão
Which is true about the Berkeley algorithm?
Responda
-
Uses averaging approach to correct clocks
-
Daemon tells each node how to adjust its clock
-
Servers are divided into strata reflecting the accuracy of their clocks
-
Lower stratum servers are assumed to be more accurate => A will try to synchronise with B’s clock
Questão 12
Questão
Which of the following is false about superpeers
Responda
-
Large-scale systems may require many local coordinators, creating the need for superpeers
-
Should offer low-latency access to other superpeers
-
Serve no more than a set number of regular nodes
-
Can be selected by reserving a fraction of the identifier space in a distributed hash table containing all nodes
Questão 13
Questão
In the ring election algorithm with nodes 1,2,3,4,5,6,7 if 7 is the coordinator and 5 and 2 both notice which node becomes the new coordinator?
Responda
-
6
-
5
-
5 or 2
-
2
Questão 14
Questão
In a token ring mutual exclusion algorithm, how does a node respond if it currently holds the resource?
Responda
-
The token is passed on to the next node in the ring when it is finished accessing the shared resource
-
It sends a message in the opposite direction back to the requester stating that it holds the lock
-
It sends a message in the forward direction to the requester stating that it holds the lock
-
The previous node sends a message back to the requester when it doesn't get a response from the node holding the resource
Questão 15
Questão
In a regular distributed mutual exclusion system, how does a node reply if it currently holds the resource?
Responda
-
It ignores the message
-
It sends a NACK response
-
It queues the message until it is finished with the resource then replies OK
-
It replies to the next node in the token ring
Questão 16
Questão
Which of these is not an advantage of centralised mutual exclusion?
Responda
-
easy to implement
-
low message overhead
-
fair (access requests are processed in order)
-
improves performance with high message volumes
Quer criar seus próprios Quizzes gratuitos com a GoConqr? Saiba mais.