caching-strategy

Caching Strategy

Overview

Caching trades freshness for speed. The hard part isn't adding a cache — it's invalidating it correctly.

Core principle: Cache at the right layer, with the right TTL, and a clear invalidation strategy.

When to Use

• Slow API responses that serve repeated data
• High database load from identical queries
• Static assets delivery optimization
• Reducing third-party API calls

Cache Layers (top to bottom)

Layer	TTL	Best For
CDN (Cloudflare, CloudFront)	Hours-days	Static assets, public pages
HTTP cache (browser)	Minutes-hours	API responses, images
Application cache (Redis/Memcached)	Seconds-minutes	DB query results, computed data
In-process (memoization)	Request lifetime	Expensive computations within a request

Cache-Aside Pattern (most common)

1. Check cache for key
2. Cache hit → return cached value
3. Cache miss → fetch from source, store in cache, return

Invalidation Strategies

Strategy	How	Use When
TTL expiry	Set expiration time	Data can be slightly stale
Write-through	Update cache on every write	Strong consistency needed
Event-driven	Invalidate on data change event	Microservices, async systems
Cache tags	Tag entries, purge by tag	Related data changes together

HTTP Cache Headers

# Immutable static assets (hashed filenames)
Cache-Control: public, max-age=31536000, immutable

# API responses (revalidate)
Cache-Control: private, max-age=0, must-revalidate
ETag: "abc123"

# No caching
Cache-Control: no-store

Anti-Patterns

Pattern	Problem
Cache everything	Stale data bugs, memory waste
No TTL	Cache grows forever
Cache without invalidation plan	Stale data served indefinitely
Caching user-specific data in shared cache	Data leaks between users
Cache stampede	All caches expire simultaneously → DB overload

Redis Quick Reference

SET user:123 '{"name":"..."}' EX 300    # 5 min TTL
GET user:123
DEL user:123                              # Invalidate

Integration

• magic-powers:performance-optimization — identify what to cache via profiling
• magic-powers:infrastructure-review — review cache infrastructure
• magic-powers:database-optimization — reduce DB load with query caching