Caching is the cheapest optimization until it's wrong. The challenge: invalidation. Use appropriate strategies: TTL, write-through, event-based, or cache-aside. In Node.js/Python with Redis, the skill is knowing when to cache and when not to.
When to Use
- Performance troubleshooting: DB queries are slow
- Designing read-heavy systems (dashboards, reports)
- Reducing load on expensive resources (external APIs, complex calculations)
Decision Framework for Redis, Memcached, or In-Memory Cache
- Cache-Aside (Lazy Loaded). Check cache; miss = load from DB, update cache, return. Simple, but cache miss is slow. Use for non-critical data.
- Write-Through. Write to cache and DB together. Ensures cache is always fresh, but slightly slower writes.
- TTL (Time-To-Live) for simplicity. Cache expires after N seconds. Reloads on next miss. Use for data that changes infrequently.