2023/12/4 11:30 Assignment 3
Assignment 3
Due 10 Nov by 23:59 Points 100 Submitting an external tool
Assignment 3 - Paxos
Marks
For undergraduates, the marks awarded for this assignment are worth 30% of the total mark for
DS. For postgraduate students, the marks awarded for this assignment are worth 20% of the total
mark for DS.
PLEASE NOTE: If your code does not compile and run the awarded mark is an automatic zero.
Our expectation is that you are able to code and submit a tested and working copy of your code.
There will not be any partial marks and you are expected to debug and fix errors and test that your
code compiles on Gradescope.
Assignment Description
Objective
To gain an understanding of consensus and voting protocols in the presence of failures of one or
more of the participants.
Welcome to the Adelaide Suburbs Council Election!
This year, Adelaide Suburbs Council is holding elections for council president. Any member of its
nine person council is eligible to become council president.
Member M1 – M1 has wanted to be council president for a very long time. M1 is very chatty over
social media and responds to emails/texts/calls almost instantly. It is as if M1 has an in-brain
connection with their mobile phone!
Member M2 – M2 has also wanted to be council president for a very long time, except their very
long time is longer than everybody else's. M2 lives in the Adelaide Hills and thus their internet
connection is really poor, almost non-existent. Responses to emails come in very late, and
sometimes only to one of the emails in the email thread, so it is unclear whether M2 has
read/understood them all. However, M2 sometimes likes to work at Sheoak Café. When that
happens, their responses are instant and M2 replies to all emails.
2023/12/4 11:30 Assignment 3
Member M3 – M3 has also wanted to be council president. M3 is not as responsive as M1, nor as
late as M2, however sometimes emails completely do not get to M3. The other councillors suspect
that it’s because sometimes M3 goes camping in the Coorong, completely disconnected from the
world.
Members M4-M9 have no particular ambitions about council presidency and no particular
preferences or animosities, so they will try to vote fairly. Their jobs keep them fairly busy and as
such their response times will vary.
How does voting happen: On the day of the vote, one of the councillors will send out an
email/message to all councillors with a proposal for a president. A majority (half+1) is required for
somebody to be elected president.
YOUR TASK:
Write a program that implements a Paxos voting protocol for Suburbs Council President that is
fault tolerant and resilient to various failure types, some of which are shown in the above.
Communication happens via sockets*. You are responsible for the message design.
*It is strongly recommended that communication happen via sockets. Other possible solutions
include RPC and inter-thread/process communication. They are needlessly complex for this
solution and can lead to implementation headaches.
Assessment
Your assignment will be marked out of 100 points, as following:
10 points - Paxos implementation works when two councillors send voting proposals at the
same time
30 points – Paxos implementation works in the case where all M1-M9 have immediate
responses to voting queries
30 points – Paxos implementation works when M1 – M9 have responses to voting queries
suggested by several profiles (immediate response, small delay, large delay and no response),
including when M2 or M3 propose and then go offline
20 points – Testing harness for the above scenarios + evidence that they work (in the form of
printouts)
10 points for the quality of your code:
Code Quality Checklist
Do!
o write comments above the header of each of your methods, describing
o what the method is doing, what are its inputs and expected outputs
2023/12/4 11:30 Assignment 3
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o describe in the comments any special cases
o create modular code, following cohesion and coupling principles
Don’t!
o use magic numbers
o use comments as structural elements (see video)
o mis-spell your comments
o use incomprehensible variable names
o have long methods (not more than 80 lines)
o allow TODO blocks
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