Design a disk-backed KV store under contention

## System Design Design a **key–value store** where: - Values can be **very large**, so they must be stored primarily on **disk**. - The interviewer is especially focused on how you handle **high contention** (many concurrent readers/writers, potentially hot keys). ### Requirements Specify and design for: - APIs: `Put(key, value)`, `Get(key)`, `Delete(key)` (optionally `CAS/CompareAndSet`). - Durability guarantees (what is acknowledged on `Put`?). - Concurrency: many threads/clients can call APIs simultaneously. - Correctness expectations under concurrent access. ### What to cover - On-disk data layout and indexing strategy. - Caching strategy. - Write path (including durability) and read path. - Techniques to reduce lock contention / handle hot keys. - How you would implement `acquire/release` locking (or alternatives).