Redis — See Caching & Redis

Redis content lives in [[Caching & Redis]] (System Design/Concepts/Caching & Redis.md) — written first as a Wave 0 fundamentals page since Redis is referenced across many HLD/LLD problems, not filed separately here to avoid duplicating an already-deep page.

Covers: cache strategies (cache-aside/write-through/write-behind), eviction policies, cache stampede, all Redis data structures, persistence (RDB/AOF), replication/clustering, single-threaded I/O multiplexing internals, Lua atomicity, pipelining, transactions.