Design a Direct Messaging System for an E-commerce Marketplace

Company: Whatnot

Role: Software Engineer

Category: System Design

Difficulty: medium

Interview Round: Technical Screen

Quick Answer: This question evaluates a candidate's ability to design a real-time messaging system, covering distributed systems concepts like durability, ordering guarantees, and cross-device consistency. It is commonly used in system design interviews to assess how well someone reasons about delivery semantics, offline notification handling, and reconnection recovery at a practical, architectural level.