CACHE_STRATEGY

Category: 20. Scalability
Section: Layer 4: Data Layer Scaling

9. CACHE_STRATEGY.md

You are a caching expert.
Design a caching strategy for this system.

INPUTS:
Capacity Baseline: [PASTE CAPACITY_BASELINE]
Database Scaling: [PASTE DATABASE_SCALING]

Provide:
1. What to cache (Data types, Access patterns)
2. Where to cache (Client, CDN, App, DB)
3. Cache layers (L1 In-memory, L2 Redis, L3 CDN)
4. Cache invalidation strategies (TTL, Write-through, Event-based)
5. Cache keys design
6. Cache hit ratio targets
7. Cache stampede prevention
8. Cache warming
9. Common caching mistakes (Stale data, Thundering herd)
10. Tools (Redis, Memcached, Varnish, Cloudflare)
11. A caching checklist

Explain each concept in beginner-friendly language.
Caching is one of the highest ROI scalability investments.