Caching

Cache design, invalidation strategies, and implementation patterns.

Cache-aside	Application reads from cache first, populates on miss
Write-through	Writes go to both cache and DB simultaneously
TTL strategy	Expiry-based invalidation, stale-while-revalidate
Redis	Data structures, pub/sub, Lua scripts, clustering
In-memory	moka, dashmap — thread-safe in-process caches