Cache-aside: the app does the legwork. Read-through: the cache does.

The two patterns differ in who talks to the database on a miss. In cache-aside, the cache is only a store: the application looks, and if the entry is absent, it fetches the data from the source itself and puts it on the shelf for next time. In read-through the cache sits in front and loads from the source on its own, so the app only ever talks to the cache.

Read it once, then a question tests whether the trick stuck.