CS 5204 - Fall, 2009
Problem Set 9
15 points
Assigned: November 10
Due: November 17 (noon)
1. (8 points) In a rollback-recovery system, a recovery line represents
the set of most recent local checkpoints that form a consistent state
of the system. Can any two local checkpoints in the recovery line be
causally related? Explain.
2. (7 points) Two processes P and Q are connected in a ring using two
channels, they constantly rotate a message m, there is only one copy of
m in the system, and P send m first. Each processes's state is defined
by a (n, h) where n is the number of times it has received m and h is a
boolelan value indicating if the process currently has the message. At
a certain point, P has the message and its state is (101, true).
Immediately after sending m, P initiates the shapshot algorithm. Give
the possible global state(s) recorded by the global state recording
algorithm. Illustrate the scenario leading to each state.