Understanding Redis Persistence: RDB vs AOF Explained

Redis provides two persistence mechanisms: RDB and AOF.

RDB (Redis Database Backup)

RDB creates a compressed binary snapshot of the in‑memory dataset and saves it to disk. The snapshot can be generated manually with SAVE (blocking) or BGSAVE (non‑blocking child process), or automatically via the save configuration option, which triggers a BGSAVE when any of the defined time‑and‑change thresholds are met (e.g., 900 seconds with at least 1 change, 300 seconds with 10 changes, 60 seconds with 10 000 changes).

AOF (Append‑Only File)

AOF records every write command to a log file, similar to MySQL binlog. The file can be flushed to disk using three policies:

appendfsync always – fsync after every command (slow but safest).

appendfsync everysec – fsync every second (fast, may lose up to one second of data).

appendfsync no – rely on the operating system (fastest, least safe).

The default and recommended setting is appendfsync everysec, offering a balance between performance and durability.

Data Recovery

When Redis starts, it automatically loads an existing RDB file if present; the server blocks until the load completes. If AOF is enabled, Redis loads and replays the AOF file by reading each command, creating a simulated client, and executing the commands sequentially. When both RDB and AOF are enabled, AOF takes precedence during recovery.