What is database replication?

Replication copies data from one database server (primary/master) to one or more replica servers (secondary/slave) to improve availability, read scalability, and disaster recovery. Types: Synchronous replication — primary waits for replicas to confirm before committing (strong consistency, higher write latency). Asynchronous replication — primary commits immediately, replicas catch up (lower latency, risk of data loss on failover). Use cases: read replicas serve SELECT queries to distribute load; standby replicas for failover; geo-distributed replicas for low-latency global access. Replication does not replace backups — a corrupt write replicates to all replicas.