How Uber Serves over 150 Million Reads per Second from Integrated Cache
Uber's CacheFront system serves over 150 million database reads per second using Redis while maintaining strong consistency. The system uses a three-layer architecture with Query Engine, Storage Engine, and integrated caching. Initial challenges included cache invalidation delays and stale data from conditional updates. Uber solved this by implementing soft deletes, monotonic timestamps, and synchronous write-path invalidation alongside asynchronous CDC (Flux) and TTL expiration. This triple-defense strategy achieves 99.9%+ cache hit rates with near-zero stale values, even with 24-hour TTLs.