COMP212 May 2007 exam: answers
Question 1 A. Give four examples of resources to be shared in a distributed system. 2 marks Possible examples are: hardware resources (disk space, printers, memory, CPU power, etc) and data/software resources (distributed ob
Trust and Security
A system is either secure or it is not.
Whether a user considers a systems to be secure is
a matter of trust.
Dicult to get right, impossible to get perfect!
Regardless of which consistency model is chosen, we
need to decide where, when and by whom copies
of the data-store are to be placed.
Replica Placement Types
There are thr
Consistency and Replication
Why Replicate Data?
guarantees correct behaviour in spite of certain faults
(can include timeliness)
While at least one server has not crashed,
More on Cryptography
Authentication Using a Shared S
A distributed system is a system in which I cant do
my work because some computer that Ive never
even heard of has failed.
Image from Wikipedia
Election & Mutual Exclusion
Many Distributed Systems require a single
process to act as coordinator (for various
Time server in the Berkleys algorithm
Designing Secured DS
Security in a distributed system must be easy to maintain. Who has authority to
perform which transactions, what are the public/private keys
3. Reliable Group Communication
Reliable multicast services guarantee that all messages are delivered
to all members of a process group.
Sounds simple, but is surprisingly tricky (as multicasting
What Can Go Wrong
Updating a replicated database: Update 1 adds 100 euro
to an account, Update 2 calculates and adds 1% interest to
the same account.
Clock reading might be diere
Introduction to Transactions
A distributed system is a collection of
independent computers that appears to its users
as a single coherent system.
To do so, they have to cooperate, that is