Caching Strategies: Improving Application Performance
Caching stores copies of data in a fast-access layer to avoid repeating expensive operations — database queries, API calls, or complex computations. Well-implemented caching can dramatically improve application performance and reduce infrastructure costs; poorly implemented caching introduces subtle bugs and stale data issues.
Types of Caching
- Browser caching: HTTP cache headers (Cache-Control, ETag) instruct browsers to cache static assets locally — eliminates network requests for unchanged assets
- CDN caching: Content Delivery Networks cache content at edge nodes geographically close to users — reduces latency and origin server load for static assets and cacheable dynamic content
- Application caching: In-memory caches (Redis, Memcached) store frequently accessed data — database query results, computed values, session data
- Database query cache: Some databases cache query results internally (though this is less relied upon in modern databases)
- Full-page caching: Complete HTML page output cached and served without executing application code — highest performance but lowest flexibility
Cache Invalidation
Cache invalidation — deciding when to remove or update cached data — is one of the classic hard problems in computer science. Strategies include: time-based expiry (TTL), event-based invalidation (invalidate the cache when the underlying data changes), and cache versioning (changing the cache key when content changes, eliminating the need to delete old keys).
Cache Anti-Patterns
- Caching personal or sensitive data without appropriate access controls
- Caching without considering cache stampede: When a cache expires, many requests simultaneously hit the origin
- Over-caching: Caching data that changes frequently — users see stale data