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How do you enable keyspace notifications in Redis, and what do the different configuration character options represent? 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? What performance considerations should you keep in mind when enabling keyspace notifications on a high throughput Redis instance?
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How would you build a reliable cache invalidation system using keyspace notifications, while accounting for their delivery limitations?

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You would use keyspace notifications as a fast, best effort mechanism to quickly invalidate related cache entries, but combine it with a periodic reconciliation process that independently verifies cached data against the source of truth, ensuring that even if a notification is occasionally missed, stale data does not persist indefinitely.
SUBSCRIBE __keyevent@0__:set
-- On notification, invalidate related cache entries
-- A separate periodic job also double checks cache freshness
Real-world example An e-commerce platform uses keyspace notifications for fast, immediate cache invalidation when product data changes, while also running an hourly reconciliation job that catches any rare cases where a notification might have been missed.

Common follow-ups: How often should a reconciliation job run to catch missed notifications without adding excessive overhead?;What other guaranteed delivery mechanisms could replace Pub/Sub for this purpose?

Streams;Caching Patterns
All 7 Keyspace Notifications questions