Database replication copies data from a primary server to one or more replicas, enabling read scaling, geographic distribution, and automated failover. The choice between synchronous and asynchronous replication affects both performance and data durability guarantees.
Replication Topologies and Trade-offs
Asynchronous replication offers minimal performance impact on the primary but risks data loss during failover because replicas may lag behind. Synchronous replication guarantees zero data loss but adds write latency equal to the network round-trip time to the replica.
Semi-synchronous replication, available in MySQL, provides a middle ground by waiting for at least one replica to acknowledge receipt before committing on the primary. This balances durability and performance for most production workloads.
Monitor replication lag continuously with alerting thresholds appropriate for your application's consistency requirements. Lag can spike during heavy write periods or when replicas perform maintenance operations, and your application logic may need to account for temporarily stale reads.