Yijia demonstrated clear structure, strong breadth across requirements, and thoughtful trade-off discussions. Timing and communication were well-managed, and he connected architectural choices to reliability and scalability concerns.
Areas of Strength
- Enumerated all functional requirements, including the special case of threads.
- Listed non-functional requirements with concrete metrics.
- Balanced CAP theorem trade-offs, prioritizing availability while addressing consistency nuances in group chat and multi-device management.
- Effective comparison of communication protocols.
- Detailed high-level design for send-message flow (WS server vs. chat server, schemas, etc.).
- Illustrated offline-to-online recovery flow with inbox table setup.
Areas for Improvement
- Expand on data durability and message lifecycle (TTL, archival, compaction, cold storage).
- Covered delete message behavior for both online and offline scenarios.
- Justified DynamoDB choice for availability (high write throughput, minimal joins).
- Mapped multi-device considerations to user-level granularity.
- Balanced CAP theorem trade-offs, prioritizing availability while addressing consistency nuances in group chat and multi-device management.
- Illustrated offline-to-online recovery flow with inbox table setup.
- Covered delete message behavior for both online and offline scenarios.
- Justified DynamoDB choice for availability (high write throughput, minimal joins).
- Mapped multi-device considerations to user-level granularity.
Suggestions
When choosing between architectural options, tie the decision to real incidents and metrics from past experience. Explain the problem, your approach, and the measurable impact—this signals practical judgment and ownership, which is highly persuasive for interviewers from OpenAI.
