Redis Persistence: Snapshot and AOF

Introduction

Redis provides two primary mechanisms for persisting data: RDB (Redis Database Backup Snapshots) and AOF (Append-Only File). These mechanisms help ensure data durability and recovery in case of failures.

1. RDB (Snapshot-Based Persistence)

RDB persistence takes snapshots of your dataset at specific intervals and saves them to disk. This method is efficient for backups and fast recovery.

Advantages of RDB:

• Efficient Storage: RDB files are compact and take up less disk space.
• Fast Recovery: Since snapshots contain the full dataset, they load quickly.
• Ideal for Backups: Suitable for periodic backups without affecting performance.

Disadvantages of RDB:

• Data Loss Risk: Data between snapshots may be lost if Redis crashes.
• Not Ideal for High Availability: Not suitable for real-time persistence.

Configuring RDB Persistence

Redis saves RDB snapshots based on configured rules in redis.conf.

save 900 1    # Save every 900 seconds if at least 1 key changed
save 300 10   # Save every 300 seconds if at least 10 keys changed
save 60 10000 # Save every 60 seconds if at least 10,000 keys changed

You can also manually trigger an RDB snapshot with:

SAVE  # Blocks Redis until the snapshot is complete
BGSAVE  # Runs in the background to avoid blocking

To disable RDB persistence, comment out or remove the save directives in redis.conf.

2. AOF (Append-Only File Persistence)

AOF logs every write operation, ensuring minimal data loss in case of failures.

Advantages of AOF:

• Better Durability: Logs every write operation, reducing data loss.
• More Control: Supports different persistence modes (always, every second, no-sync).
• Readable Log Format: AOF logs can be manually edited for recovery.

Disadvantages of AOF:

• Larger File Size: AOF files grow significantly compared to RDB.
• Slower Recovery: Requires processing all logged commands on restart.

Configuring AOF Persistence

To enable AOF persistence, edit redis.conf:

appendonly yes  # Enable AOF
appendfsync everysec  # Sync to disk every second (balanced performance)

You can also trigger a manual AOF rewrite to reduce file size:

BGREWRITEAOF  # Background rewrite to optimize AOF file size

To disable AOF, set:

appendonly no

3. Choosing Between RDB and AOF

Hybrid Approach

Redis allows using both RDB and AOF together for a balance between speed and durability. To enable both, configure:

save 900 1
appendonly yes

Conclusion

Redis persistence ensures data durability and recovery. While RDB provides efficient backups, AOF offers better durability. Choosing the right persistence method depends on your application’s needs.

For high-performance applications, combining RDB and AOF provides the best balance between speed and reliability.