In the cache-aside caching pattern, what happens on a cache miss?

• A. Return a null response to the caller.
• B. Continuously poll the cache until data appears.
• C. Load the data from the underlying source of truth and populate the cache.
• D. Preload all data into the cache at startup.

Answer: (C)

In cache-aside, when the data isn’t in the cache (a cache miss), the system fetches it from the underlying source of truth (like the database), stores that data in the cache, and then returns it to the caller. This on-demand loading keeps the cache warm only with what’s actually needed, rather than preloading everything or waiting for something else to fail first. That’s why loading from the primary data store and populating the cache best fits the miss scenario. The other options describe behaviors that don’t align with the lazy, on-demand nature of this pattern: returning null avoids the data the caller expects, polling wastes time and resources, and preloading all data at startup contradicts the on-demand philosophy.