Four Layers of Rails Caching: Stop Running Queries You Already Answered

A Rails developer explains how to cache expensive database queries using four layers: compute caching with Rails.cache.fetch, key-based invalidation, fragment caching for views, and HTTP caching. The example shows an 800ms shipment ranking query that can be served in milliseconds after caching. The post emphasizes using updated_at as a version key to automatically expire caches when data changes.