Caching is great until a key expires. When a highly popular key (like the homepage payload) expires under a load of 5,000 requests per second, all 5,000 requests miss the cache simultaneously and hit the database. This is a cache stampede, and it can bring down a database in seconds.
We experienced this during a high-traffic sports scoring event. When our cache TTL expired, the database was hit with thousands of identical, heavy SQL queries, causing thread exhaust and downtime.
We implemented XFetch, a probabilistic early expiration algorithm. When a request is read near the expiration threshold, the system probabilistically recalculates the value in the background before the key actually expires. The database is only ever queried once, and the cache remains hot.
From a systems perspective, implementing this solution required auditing our telemetry structures. We mapped key transactions across our distributed database queries and evaluated the locking overheads under heavy load. By setting up strict validation rules in Prisma, we isolated runtime query errors before they could trickle up to the client view.
Ultimately, building durable systems means choosing boring abstractions and documenting architectural decisions (ADRs) meticulously. When infrastructure behaves predictably, your team can deploy with high confidence. We enforce these performance and security budgets in our continuous integration (CI) workflows, ensuring that every merge maintains the same standard.