Chapter 4 of 10All chapters
Chapter 4 of 10
Caching
The cheapest speedup and the subtlest bugs.
Where caches live
In the browser, at a CDN, in front of the application, inside it, and in front of the database. Each layer removes work from everything behind it.
- Cache what is expensive and read often, not everything.
- A cache hit rate below about 80 percent rarely justifies the complexity.
Invalidation
The hard question is when a cached answer stops being true. Short expiry times are simple and slightly stale; explicit invalidation is exact and easy to get wrong.