The common mistake: build without a caching strategy, discover certain operations are slow under load, start adding caches reactively. The reactive cache is almost always in the wrong layer, invalidated incorrectly, and creates consistency bugs.
Define your caching strategy during architecture design. For every piece of data: what is its read-to-write frequency? What is the acceptable staleness window? What is the correct invalidation trigger?
The most important principle: cache the computed result, not the raw data. Caching a database row saves one query. Caching a rendered page fragment saves the query, the transformation logic, and the template rendering.
Design your cache invalidation triggers at the same time as your cache entries.
— Dick Bassey | DevDick | 2024