PlanetScale database clusters use traditional MySQL replication, with each node containing a copy of the data it needs to operate properly. Clients connect to the source MySQL server for writes, and clients with read-only workloads can connect to one of the replicas. Aurora's replication system is proprietary and stores redo log entries on dedicated storage appliances in the same availability zone as the source compute node. Data is replicated on the storage level, allowing read-only compute nodes to be started at any time without affecting primary data access. PlanetScale excels with its open-source software foundation built on Vitess, a proven MySQL-compatible and horizontally scalable project, offering features like rolling MySQL upgrades, sharding, and automatically validated backups.