Quiz 7 Flashcards
Causal relationships can be deduced by using
Absolute clock
Lamport clock
Vector clock
Vector clock
Consider the following sequence of events at processes p0, p1 and p2: where si and ri are corresponding send and receive events for i=1,2,3
What are the Lamport clock values for r1, s1, a, and s2?
p0: s1 . a . b
p1: c . r1 . s2
p2: d r2 . e
r1=1, s1=0, a=2, s2=3
r1=2, s1=1, a=2, s2=3
r1=1, s1=0, a=1, s2=2
r1=1, s1=1, a=2, s2=2
r1=2, s1=1, a=2, s2=3
Consider the following sequence of events at processes p0, p1 and p2: where si and ri are corresponding send and receive events for i=1,2,3
What are the Vector clock values for r1 and e?
p0: s1 . a . b
p1: c . r1 . s2
p2: d r2 . e
r1=(1 2 0), e=(1 3 3)
r1=(2 1 0), e=(3 1 1)
r1=(1 1 0), e=(2 0 2)
r1=(1 2 0), e=(1 3 3)
Which of the mutual exclusion algorithms has N points of failure?
Token-ring
Centralized
Distributed
Decentralized
Distributed
Centralized mutual exclusion algorithm may suffer from scalability problem
False
True
True
In clock synchronization:
Accuracy is keeping the deviation between the clocks of two machines in a distributed system within a specified bound
Precision is keeping the difference between the UTC and the clock for a machine bound to a threshold value
Accuracy is keeping the difference between the UTC and the clock for a machine bound to a threshold value
Precision is keeping the deviation between the clocks of two machines in a distributed system within a specified bound
Accuracy is keeping the difference between the UTC and the clock for a machine bound to a threshold value
Precision is keeping the deviation between the clocks of two machines in a distributed system within a specified bound
The idea behind Lamport’s logical clock is/are that:
Processes can use the order of occurrence of events rather than their absolute time occurrences
Processes can use the absolute timestamp to order their events
Processes can use the order of occurrence of events rather than their absolute time occurrences
Given two Lamport’s logical clocks C(a) and C(b) corresponding to events a and b respectively.
Which of the following statements can be true?
If events a and b happen in the same process, and C(a) < C(b), then a → b.
If a and b happen in different processes and C(a) < C(b) then a→b
If a is the sending of a message, and b is the receipt of that message, then a → b and C(a) < C(b)
If events a and b happen in the same process, and C(a) < C(b), then a → b.
If a is the sending of a message, and b is the receipt of that message, then a → b and C(a) < C(b)
Given two events a and z, with Lamport clocks C(a) and C(z) and their Vector clocks V(a) and V(z). What condition is necessary to conclude that event a happened before event z?
a happened before z if V(a) < V(z)
a happened before z if C(a) > C(z)
a happened before z if V(a) > V(z)
a happened before z if C(a) < C(z)
a happened before z if V(a) < V(z)
Which of the mutual exclusion algorithms requires 2.(N-1) messages for a process to enter its critical region where N is the total number of processes?
Decentralized
Token ring
Distributed
Centralized
Distributed
