CMPSCI 677: Homework 3
Due: Friday, April 1 2005, 5pm
Offcampus students: one week from when you view Lecture 13
Web posted: Saturday, March 26 2005

Describe the benefits of a twolevel scheduler implementation of threads
as compared to a userlevel and kernellevel threads implementation.

Consider the iterative and recursive name resolution techniques
and klevel hierarchy of name servers.
 If the oneway cost of communicating from a client to a server is 'C'
and oneway 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
distributed events,
show that if V(a) < V(b) then a>b and viceversa , 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
strict 2PL?
 Explain why writeahead logs are prefered to private workspaces in commercial transcational systems?
Prashant Shenoy
Puru Kulkarni