Consistency

HTTP caching (Cache-Control, ETag, fresh/stale, immutable static resources); reverse proxies; application-layer: side vs inline cache, LRU eviction, TTL, local vs external cache, thundering herd, cascading failure; 80% hit rate as scalability threshold

CAP theorem and PACELC extension; Kleppmann's critique ("best avoided"); timeliness vs integrity distinction

When to use linearizability vs causal vs eventual consistency; timeliness vs integrity distinction; decision guide by scenario (locks, balances, feeds, shopping carts, multi-region); read routing as the practical knob; CAP trap warning

Full spectrum: linearizability, sequential, causal, strong eventual, eventual; COPS causal+ implementation; isolation levels; linearizability ≠ serializability; timeliness vs integrity; safety vs liveness

Conflict-free Replicated Data Types; semilattice + LUB merge; strong eventual consistency; LWW/MV registers; CALM theorem (application-level consistency, not linearizability)

ACID, 2PL, OCC, MVCC, 2PC, Spanner, Saga, Outbox; XA limitations; coordination-avoiding correctness; Newman's "just say no" to 2PC during migration

Hierarchical resolution process; TTL trade-offs; DNS as eventually consistent KV store; DNS as SPOF; static stability principle

State machine replication (Raft), chain replication (head/tail topology, failure modes, data/control plane split), leader-follower, Dynamo-style; replication lag anomalies; multi-leader conflict resolution

Distributed transactions via local transactions + compensations; 8 saga type taxonomy; semantic vs implementation coupling; orchestration/choreography trade-offs; DDD: saga vs process manager distinction; stateless/stateful saga; process manager as aggregate; Newman: backward/forward recovery, semantic rollbacks, step reordering, team-based coordination choice