Design a KV store with transactions

## System Design Prompt Design an in-memory/disk-backed **key-value store** that supports **transactions**. ### Functional requirements - Basic operations: `Get(key)`, `Put(key, value)`, `Delete(key)` - Transactions: - `Begin()` - `Commit()` - `Rollback()` - Multiple concurrent clients. ### Transaction semantics (clarify in interview) - At minimum: atomicity and isolation within the store. - Define isolation level target (e.g., Read Committed or Snapshot Isolation). ### Non-functional requirements - Reasonable performance under concurrent access. - Durability (optional depending on scope): data survives crashes. - Support for large datasets (may exceed memory). ### Deliverables - APIs - Data model and storage layout - Concurrency control approach - Crash recovery approach (if durability is required) - Complexity and key trade-offs