Fast, Maybe True: The Two Sources of Truth Dilemma
Caching is frequently treated as a universal cure for slow systems, but introducing a cache creates two conflicting sources of truth.
01.The Speed vs Freshness Trade-off
A fast wrong answer is worse than a slightly slower correct answer. When Cache Guy returns a stale permissions matrix or outdated product inventory, business logic fails silently while dashboard latency charts look beautifully green.
02.Cache Invalidation & Stampedes
Cache invalidation is notoriously difficult because distributed caches lack transactional coordination with the primary database. When thousands of concurrent requests hit an expired key simultaneously (cache stampede), the backend database collapses.
03.Resilient Caching Guidelines
1. Use probabilistic early expiration (XFetch) to prevent cache stampedes. 2. Mutate cache synchronously within database commit hooks, or use short TTLs with eventual consistency. 3. Never use a cache to mask a missing database index.
Caching creates a second copy of truth. When the primary truth updates, the cached copy becomes a high-speed lie.