Consensus: Quorum, Minority Quorum, Administered Quorum, and Beyond

Consensus protocols like Paxos and Raft are the backbone of modern distributed systems — but their purpose, limitations, and trade-offs are often misunderstood. And what exactly defines a consensus protocol, anyway? This session begins with a quick overview of well-known protocols and what consensus actually guarantees — and what it doesn’t. We'll explore leader election, discovery, durability, and, notably, the quorum. We'll also examine the scalability challenges of consensus algorithms and the trade-offs they impose. From there, we’ll challenge conventional assumptions. We’ll introduce the concept of minority quorum, showing that it's not only viable but logically equivalent from a consensus perspective. We’ll then go further, illustrating what an administered quorum looks like — and how, by separating leader election from messaging, we can dramatically reduce the cost of distribution. Expect a fast-paced exercise in logic, with practical takeaways, and a little bit of controversy.

Speakers