Database Replication

Replication is copying data from one database server to one or more others and keeping the copies up to date. It protects against server failure and lets read traffic be spread across several servers.

In primary-replica (master-slave) replication, all writes go to the primary and are copied to read-only replicas. Copying can be synchronous (safer, slower) or asynchronous (faster, but replicas may lag slightly). Multi-primary setups accept writes on several servers but must resolve conflicts. Replication copies the whole dataset, unlike sharding, which splits it.