4.Replication

Why distributed systems keep multiple replicas of the same data, how replication improves availability and read capacity, and the major design dimensions behind replication.

Why multiple leaders are useful across regions or offline-capable systems, and how concurrent writes create conflicts that require prevention, detection, or resolution.

Leaderless replication with multi-replica reads/writes, quorum-style coordination, version reconciliation, read repair, and anti-entropy.

How leader/follower replication handles writes, reads, initial synchronization, incremental catch-up, leader election, and failover.

Physical and logical change logs, statement- versus row-oriented replication, and why deterministic replay and schema/storage coupling matter.

Synchronous, asynchronous, and semi-synchronous replication and how acknowledgement rules change latency, durability, availability, and replica lag.

The three common replication topologies: single-leader, multi-leader, and leaderless replication, and the trade-offs each introduces.