Persistence: RDB and AOF

Why Persist at All

Redis keeps data in memory, so a restart would lose everything unless persistence is configured. Two mechanisms exist: RDB snapshots and AOF (Append Only File).

RDB Snapshots

save 900 1      # if >=1 change, save after 900s
save 300 10
dir /var/lib/redis
dbfilename dump.rdb

RDB is a compact point-in-time snapshot, perfect for backups and fast startup, but it can lose the last few minutes of writes.

AOF

appendonly yes
appendfsync everysec   # balance of flush cost and safety

AOF logs each write command and replays it on restart, losing at most the fsync window (seconds). It grows, but Redis rewrites it automatically.

Choosing a Strategy

• RDB only - fast restarts, some data loss.
• AOF only - durable, slightly slower restarts.
• Both (default since Redis 7) - snapshot plus log.

Backup Practice

Use redis-cli SAVE or BGSAVE to produce snapshots, copy them off-machine regularly, and test restoration in a staging instance.

Key Points

• RDB snapshots and AOF logs cover recovery.
• appendfsync everysec is the pragmatic default.
• Prefer both modes for production data.
• Backups must live off the Redis host too.