Empirical Study of Unstable

This thesis studies the effect of unstable leaders in Paxos protocol. Paxos algorithm is one of the most popular solutions for distributed consensus, and is often used for building replicated state machines. Safety is guaranteed by Paxos algorithm regardless of various machine and communication failures. However, the liveness is compromised when multiple Paxos leaders exist at the same time. Also, despite the extensive literature in the field, implementing Paxos algorithm for practical systems is still non-trivial. This thesis first studies the implications of multiple Paxos leaders in practical systems and provides an optimization by using leases. A complete specification of classical Paxos protocol is provided. We evaluate our implementation and show the effect of unstable leaders in practical systems.