The basic set/get part took maybe five minutes.
Start by clarifying requirements and constraints, then design a simple in-memory key-value store with a transaction stack to support begin, commit, and abort. Discuss trade-offs between different implementation strategies (e.g., copy-on-write vs. undo logs) and analyze time/space complexity. Finally, walk through an example to demonstrate correctness.
Pro tip: Mention that you would use a stack of transaction contexts to handle nested transactions, and discuss how to ensure atomicity and isolation. Also, proactively address edge cases like aborting without an active transaction or committing an empty transaction.
Ask about expected operations, concurrency needs, persistence, and whether nested transactions are required. Confirm that the store is in-memory and single-threaded unless specified otherwise.
Propose a main hash map for committed data and a stack of transaction contexts. Each context can store pending changes or use copy-on-write for isolation.
Define set to write to the current transaction (or main store if none). Begin pushes a new context; commit merges the top context into the parent or main store; abort discards the top context.
Compare copy-on-write (simple but memory-heavy) vs. undo logs (memory-efficient but complex). Discuss time complexity for each operation and space overhead.
Walk through a sequence of operations including nested transactions to verify correctness and edge cases. Mention potential optimizations like lazy copying.
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