CMPSCI 677: Homework 3
Due: Friday, April 1 2005, 5pm
Off-campus students: one week from when you view Lecture 13
Web posted: Saturday, March 26 2005
Describe the benefits of a two-level scheduler implementation of threads
as compared to a user-level and kernel-level threads implementation.
Consider the iterative and recursive name resolution techniques
and k-level hierarchy of name servers.
- If the one-way cost of communicating from a client to a server is 'C'
and one-way cost of communicating amongst servers is 'S',
determine the cost of name resolution using each of the techniques.
- State the conditions under which each one of them is better than
the other, or if one is always better and reasons for same.
- Give an example to show that Lamport's clock
does not give us the following property:
if C(a) < C(b) then a -> b, where a and b are events,
and C(i) is the clock value assigned to event i.
- Assume vector clocks used for vector ordering, and 'a' and 'b' are
show that if V(a) < V(b) then a->b and vice-versa , i.e.,
if a->b then V(a) < v(b)
What is the differnce between Weak and Strong mobility?
Give example situations where each one of them can be useful.
In the Ring algorithm for leader election, more than one elections can be
in operation concurrently in a group. While this does not effect correctness,
nodes send election messages more than once and still elect the same leader.
Suggest a modification to the algorithm to make it more efficient
by reducing number of messages transmitted during concurrent elections.
- What is the advantage of using strict two phase
locking over normal two phase locks? What might be a disadvantage of
- Explain why write-ahead logs are prefered to private workspaces in commercial transcational systems?