How does Rails handle large-scale multi-level caching with request coalescing and stampede protection?

Rails prevents cache stampedes using request coalescing, mutex locks, and probabilistic early refresh strategies.

Cache stampedes occur when many requests simultaneously miss cache and overload the database. Rails mitigates this using mutex locks (e.g., Redis SETNX), request coalescing (single flight pattern), and early refresh strategies that regenerate cache before expiration. This ensures system stability under high concurrency.