Persistence

By default, Redis stores all data in memory. When the server stops, the data is gone. Redis offers two persistence mechanisms — RDB (Redis Database) snapshots and AOF (Append-Only File) — so that data survives restarts. You can use either or both.

RDB — Point-in-Time Snapshots

RDB persistence saves the entire in-memory dataset to a binary snapshot file (usually named dump.rdb) at configured intervals.

Configure snapshot rules in redis.conf:

# Save after 900 seconds if at least 1 key changed
save 900 1
# Save after 300 seconds if at least 10 keys changed
save 300 10
# Save after 60 seconds if at least 10000 keys changed
save 60 10000

Trigger a manual snapshot:

# Blocking save — blocks the server until complete
127.0.0.1:6379> SAVE

# Non-blocking save — forks a child process to save in background
127.0.0.1:6379> BGSAVE

Advantages of RDB: Compact single-file backups, fast restart (loading binary snapshot is fast), minimal performance impact (background fork).

Disadvantage: You can lose data written since the last snapshot (up to several minutes of writes).

AOF — Append-Only File

AOF logs every write command to a file. On restart, Redis replays the AOF to rebuild the dataset.

Enable AOF in redis.conf:

appendonly yes
appendfilename "appendonly.aof"

Control how often AOF is fsynced to disk:

# always — safest, slowest (fsync every write)
appendfsync always

# everysec — default, good balance (fsync every second)
appendfsync everysec

# no — fastest, least safe (OS decides when to flush)
appendfsync no

Advantages of AOF: Far less data loss risk (everysec loses at most 1 second of writes), human-readable command log.

Disadvantage: AOF files are larger than RDB files; replay can be slower on large datasets.

AOF Rewrite

Over time, the AOF grows. Redis can compact it by rewriting only the minimal set of commands needed to reconstruct the current state:

127.0.0.1:6379> BGREWRITEAOF

Using Both RDB and AOF

You can enable both mechanisms simultaneously. Redis recommends this for the best durability: RDB for fast backups, AOF for minimal data loss.

No Persistence Mode

For a pure cache where data loss is acceptable, disable all persistence:

# In redis.conf
save ""
appendonly no

Choosing the right persistence strategy depends on your tolerance for data loss versus your performance and storage requirements.