If an API caches user profiles, what method ensures the cache is updated immediately when a user changes their profile, rather than waiting for a timer?

The method to ensure an API cache is updated immediately when a user changes their profile, rather than waiting for a timer, is proactive cache invalidation triggered directly by the write operation that updates the user's profile. An API, or Application Programming Interface, is a set of rules and protocols for building and interacting with software applications.

Here is the process:

When a user initiates a change to their profile, the API first processes this request by updating the authoritative data source, which is the primary and most reliable storage location for the data, typically a database. This ensures the fundamental data is always current. A cache is a high-speed data storage layer that stores a subset of data, typically transient, so that future requests for that data are served faster than accessing the primary data source.

Immediately after the successful update to the authoritative data source, the API explicitly triggers a cache invalidation operation for that specific user's profile entry. Cache invalidation is the process of marking cached data as no longer valid or removing it entirely from the cache. This involves evicting the outdated user profile entry from the cache. Eviction means removing a specific item from the cache.

Consequently, the next time a request comes in to retrieve that user's profile, the API will check the cache. Since the previous entry was invalidated and evicted, this will result in a cache miss. A cache miss occurs when the requested data is not found in the cache. Upon a cache miss, the API then fetches the freshest, updated user profile data directly from the authoritative data source.

After retrieving the current data, the API stores this new, accurate version of the user profile back into the cache. This pattern ensures that subsequent read requests will benefit from the cache's speed, serving the correct, recently updated information. This approach is commonly known as a cache-aside strategy combined with write-through or write-behind invalidation.

This method guarantees immediate consistency between the authoritative data source and the cache for that specific user profile, preventing the serving of stale data that would occur if relying on a timer-based expiration, which introduces a window of time during which outdated information might be presented.