6.1 RDB Snapshots and the AOF Log

Writing enough information to disk to rebuild the dataset after a restart is called persistence. Redis needs it because it serves every request from RAM, and RAM is wiped when the process or the machine stops. Redis offers two mechanisms with different trade-offs: RDB takes periodic point-in-time snapshots of the whole dataset, and AOF (the append-only file) logs every write command.

This lesson follows one instance through both mechanisms: an order service whose Redis holds 20 GB of carts, sessions and counters and receives 5,000 writes per second