How does Redis ensure that cached data is always up to date?

Redis ensures that cached data is up to date by using cache expiration mechanisms and publishing/subscription mechanisms.

1. Cache Expiration Mechanism: When setting up caching, an expiration time can be defined for each key-value pair. When the data in the cache expires, Redis will automatically delete that key-value pair. The next time the key-value pair is accessed, a cache update operation will be triggered.
2. Redis offers a Publish/Subscribe mechanism for real-time data updates. When data changes, Redis can publish an update message to subscribers, triggering cache updates to ensure data in the cache is up to date.

By combining the use of cache expiration mechanism and publish/subscribe mechanism, it is possible to ensure that the data in Redis cache is up to date effectively.