Where Caches Live: The Full Stack

Caching is not one layer — it is a stack. At the top, the browser caches static assets (CSS, JS, images) and sometimes API responses based on HTTP headers. Below that, a CDN (Cloudflare, CloudFront, Fastly) caches content at edge locations close to users worldwide. The load balancer may cache health-check results or session affinity data.

Inside your application, an in-process cache (a Map or LRU structure in Node.js, Python, or .NET) holds hot data in the app's own memory — microseconds to access. A distributed cache like Redis or Memcached sits between the app and the database, shared across all app instances. Finally, the database itself has internal caches: PostgreSQL's buffer pool keeps frequently accessed pages in RAM, and query caches (where they exist) store result sets.

The memory hierarchy mirrors this pattern at the hardware level: CPU L1/L2/L3 cache → RAM → SSD → spinning disk → network. Each level is slower but larger. Your job as an engineer is to push data as far up the stack as possible without serving stale or inconsistent results.

Before

Single layer — every request hits the database

1User → App Server → Database → Disk2// Every request travels the full depth

After

Multi-layer cache stack

1User Request2    ↓3Browser Cache (ms)4    ↓ miss5CDN Edge Cache (10–50ms)6    ↓ miss7App In-Process Cache (μs)8    ↓ miss9Redis / Memcached (1–5ms)10    ↓ miss11Database Buffer Pool (5–20ms)12    ↓ miss13Disk (10–100ms+)

Check your understanding

List cache layers from user toward disk.Show answerHide answer
Answer
Browser → CDN → app in-process → Redis/Memcached → DB buffer pool → disk (typical stack; not every app uses all).
What is the risk of pushing data too high in the stack?Show answerHide answer
Answer
Serving stale or user-private data at a shared layer if invalidation and auth boundaries are wrong.
Is DB buffer pool a product feature you configure like Redis?Show answerHide answer
Answer
It is engine internals — tune and observe, but it is not an application cache API.