Basic Paxos in Action

We learned the rules for the basic Paxos algorithm in the previous lesson. In this lesson, we will see those rules in action by running Paxos through three different scenarios. We will also see a situation where Paxos makes no progress. Lastly, we will present a solution to making progress and a complete Paxos protocol simulation involving all three roles: proposers, acceptors, and learners. This will also show the role of learners in knowing the current status of a slot's chosen value.

Previous value already chosen

Let's see what happens when a value has already been chosen, and a new proposer comes in even with a higher proposal number. According to the rules, the new proposer is obligated to acknowledge the already chosen value and cannot enforce its own value.