Distributed Systems · Cluster
Consensus
Agreement protocols and their failure assumptions.
- 01 Why Majority Quorums Intersect and What the Intersection Buys The arithmetic of quorum overlap, why read and write sets must share a node, and what asymmetric quorum sizes cost in latency, durability, and fault tolerance.
- 02 FLP Impossibility and Why Real Protocols Assume Partial Synchrony The bivalent-configuration argument behind the FLP result, why the proof needs only one faulty process, and how partial synchrony and randomized termination step around it.
- 03 Raft Elections: Terms, Votes, and the Pre-Vote Correction How terms impose a total order on leadership attempts, why the voted-for rule plus the log-suffix check prevents two leaders in one term, and what pre-vote and check-quorum add.
- 04 Paxos Prepare and Accept: What the Promises Are For Why acceptors must promise not to accept older proposals, how the highest-numbered proposal wins a phase, and what breaks when the two phases are collapsed.
- 05 Commit Rules, Figure 8, and Why a Leader Cannot Trust Its Log Why Raft only commits entries at a term boundary, the reordered-commit scenario that defeats the naive rule, and how the commit index interacts with log repair.
- 06 Membership Change Under Joint Consensus Why a configuration cannot be edited in place, how C_old,new requires dual majorities during the transition, and what single-server changes cost in safety margin.
- 07 Snapshot Install and the Cost of Compacting a Consensus Log How snapshots bound log growth, why installing a snapshot is a different operation from sending entries, and where the boundary index and chunking interact with elections.
- 08 Why Byzantine Fault Tolerance Costs a Third of the Cluster The 3f+1 bound, where it comes from, and how quorum sizes must change when a faulty node can lie rather than merely stop.
- 09 Read Index and Leader Leases: Serving Reads Without a Log Entry Why a committed write is not yet a readable write, how a quorum heartbeat round establishes read freshness, and what a lease assumes about clocks.
- 10 Leaderless Ordering: Dependency Graphs Instead of a Single Log How per-command sequence numbers and dependency sets let replicas commit concurrently, why conflicts still impose an order, and where recovery becomes the expensive part.