All 7 Keyspace Notifications questions
More in Keyspace Notifications
What are keyspace notifications in Redis, and what do they let your application do? How do you subscribe to and handle a specific type of keyspace notification, such as being alerted whenever a key expires? What are the reliability limitations of keyspace notifications that developers should understand before relying on them for critical application logic? What practical use cases in a real application are well suited to keyspace notifications despite their delivery limitations? How would you build a reliable cache invalidation system using keyspace notifications, while accounting for their delivery limitations? What performance considerations should you keep in mind when enabling keyspace notifications on a high throughput Redis instance?
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How do you enable keyspace notifications in Redis, and what do the different configuration character options represent?

Beginner

Answer

You enable keyspace notifications using the CONFIG SET command on the notify-keyspace-events setting, combining character flags where K enables keyspace events, E enables keyevent events, and additional letters like g, s, or x specify which specific types of commands or events, such as expired keys, should actually trigger a notification.
CONFIG SET notify-keyspace-events 'Ex'
-- E enables keyevent notifications
-- x specifically enables expired event notifications
Real-world example A session management system enables notifications specifically for expired events using the Ex flag combination, keeping notification overhead minimal by not subscribing to every possible type of keyspace change.

Common follow-ups: What is the difference between keyspace and keyevent notification channels?;What happens if you enable all notification types on a very busy server?

Pub/Sub;Redis Performance Tuning & Benchmarking
All 7 Keyspace Notifications questions