高频题（0）
1. Designing a Scalable Webhook System
Design a webhook system that can handle a scale of 1 billion webhook events per day. Address the non-functional requirements that would allow such a system to operate at this scale.
2. Versioned Key-Value Store Design
Design a versioned key-value store that maintains a history of values for each key with timestamps. Explain how you would handle queries that also provide a timestamp. Discuss how you would address multi-threading and out-of-memory (OOM) issues in your design.
