In-Memory Caching

Summary

Caching data directly in your application process's memory (e.g. a JS `Map`) — the fastest option, but limited to a single server instance and lost on restart.

• 1Build a simple in-memory cache with a Map and manual TTL expiry logic.
• 2Understand why in-memory caching breaks down once you run multiple server instances.
• 3Compare it to Redis: faster, but not shared or persistent.