What is caching and why does it matter?
Caching stores a result so you don't compute or fetch it again:
- Browser cache: files stay on the visitor's device
- CDN cache: pages and assets served from a location near the visitor (Cloudflare, Vercel)
- Application cache: Redis holds expensive query results or sessions
- Database cache: materialised views for heavy reports
Why: it cuts response times and server cost dramatically. The hard part is invalidation — decide when cached data must refresh.