Otter.Ai·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jul 2026Remote

Summary

Interviewed for a software engineering role at Otter.ai and got hit with an in-memory key-value store problem that added nested transactions on top. Felt manageable at first but the nested rollback semantics tripped me up more than I expected.

Questions Asked (1)

Design and implement an in-memory key-value store that supports get, set, and delete operations, plus nested transactions that can be committed or rolled back independently.

System DesignAlgorithms & Data StructuresTechnical Trade-offs

Author's notes

The basic get/set/delete part I had down pretty fast.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then propose a design using a stack of transaction layers where each layer tracks changes relative to its parent. Implement get, set, and delete with transaction-aware logic, and discuss trade-offs between simplicity and performance.

Pro tip: Emphasize that nested transactions require a stack of change logs, and that rollback only affects the current transaction's changes, not committed data. Mention that reads should see the most recent uncommitted changes within the active transaction chain.

1. Clarify Requirements

Ask about expected operations, transaction nesting depth, concurrency needs, and whether reads within a transaction should see uncommitted changes. Confirm that transactions can be committed or rolled back independently.

2. Design Data Structures

Propose a main key-value store (e.g., hash map) and a stack of transaction layers. Each layer stores a map of keys to new values or deletion markers, and optionally a reference to the parent layer.

3. Implement Operations

For get, search from the top of the stack downwards for the key; if found, return the value or indicate deletion. For set and delete, record the change in the current transaction layer (or main store if no active transaction).

4. Handle Commit and Rollback

Commit merges the current layer's changes into its parent (or main store) and pops the layer. Rollback simply discards the current layer, reverting to the previous state.

5. Discuss Trade-offs and Optimizations

Analyze time and space complexity, and discuss alternatives like copy-on-write, persistent data structures, or lazy deletion. Mention potential concurrency issues if applicable.

Key Points to Mention

Use a stack of transaction layers to support nesting, with each layer tracking changes relative to its parent.
Reads must traverse the transaction stack from top to bottom to find the most recent value or deletion.
Commit merges changes into the parent layer; rollback discards the current layer.
Deletion can be represented as a special tombstone value to distinguish from absence.
Time complexity: O(1) for set/delete, O(depth) for get in worst case; space complexity grows with number of uncommitted changes.
Consider concurrency control (e.g., locking or optimistic concurrency) if multiple threads access the store.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.