Caching in Payment Systems

Every backend engineer has heard the advice: add a cache. It will make your system faster. And they are right, it will. But a cache that is not properly understood is one of the most effective ways to take down your entire production system, including the database it was supposed to protect. This article covers everything you need to know about caching in a payment system: what it is, how it works, the patterns that govern it, the failure modes that will wake you up at 2am, and the decisions tha