I spent the first few minutes just trying to nail down scope, which I think was the right call.
Start by clarifying requirements: in-memory vs disk-backed, isolation level, and concurrency model. Then design a core data structure (e.g., hash map with versioning) and layer transaction management using a write-ahead log or copy-on-write for rollback. Finally, address concurrency control (e.g., per-key locks or MVCC) and discuss trade-offs.
Pro tip: Emphasize that you would first define the consistency and isolation guarantees (e.g., snapshot isolation) because they drive the entire design, and mention that you'd validate with a simple test harness simulating concurrent transactions.
Ask about expected scale, durability needs, isolation level, and whether clients are threads or separate processes. This determines whether to use in-memory with periodic snapshots or a disk-backed log.
Propose a data structure like a hash map for in-memory or a B-tree/LSM tree for disk. For transactions, consider versioning (MVCC) or copy-on-write to support rollback and consistent reads.
Describe how begin creates a transaction context, commit atomically applies changes (e.g., via write-ahead log), and rollback discards uncommitted changes. Discuss how to handle nested transactions if needed.
Choose a concurrency model: pessimistic locking (per-key locks) or optimistic (MVCC with conflict detection). Explain how to ensure isolation and prevent lost updates or dirty reads.
Compare in-memory vs disk-backed in terms of latency, durability, and complexity. Cover crash recovery (e.g., replaying WAL) and how to handle partial failures.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.