Distributed Systems

CAP and PACELC, the linearizability-to-eventual spectrum, session guarantees, and why the C in ACID is not the C in CAP.

Why agreement is hard, how Raft actually works, majority quorums and split-brain, and when you truly need a distributed lock.

Leader-follower, multi-leader and leaderless topologies, sync vs async durability, quorum reads and writes, replication lag and conflict resolution.

Range vs hash partitioning, consistent hashing and virtual nodes, hot shards and skew, secondary indexes, rebalancing and request routing.

Failure detectors and heartbeats, clock skew and logical clocks, delivery semantics and idempotency, and the retry patterns that prevent cascading failure.

Two-phase commit and why it blocks, sagas and compensation, the dual-write problem and the outbox, the isolation you lose, and how modern systems get atomicity anyway.