Build a real-time Chat Pipeline
Last updated: August 4, 2025
Quick Overview
Design a real-time chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Goldman Sachs
System Design
Software Engineer
Goldman Sachs
August 4, 2025Software Engineer
Onsite
System Design
Medium
4
12
930 solved
Design a real-time chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Goldman Sachs typically last 45-60 minutes. You are expected to drive the conversation, starting from requirements gathering through to a detailed architecture. The interviewer will evaluate your ability to handle ambiguity and make practical engineering decisions.
What the Interviewer Expects
- Systematically gather requirements and estimate capacity (QPS, storage, bandwidth)
- Design a scalable architecture with clear component responsibilities
- Make well-reasoned database and caching decisions with trade-off analysis
- Address consistency vs availability trade-offs specific to the use case
- Discuss partitioning strategy, replication, and data modeling
- Cover failure handling, monitoring, and alerting strategies
Key Topics to Cover
High-level architecture and component design
Load balancing and horizontal scaling
Partitioning and sharding strategies
Failure handling and fault tolerance
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- How would you handle schema migrations with zero downtime?
- How would you handle a region-wide outage?
- How do you ensure data consistency across multiple services?
- What monitoring and alerting would you set up on day one?
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Requirements
Functional Requirements:
- Real-time Messaging: Users should be able to send and receive messages instantly.
- Group Chat Support: Ability to create and manage group chats with multiple ...
Capacity Estimation
Back-of-Envelope Calculations:
- User Base: Assume 1 million concurrent users.
- Message Rate: If each user sends an average of 10 messages/minute, the total messages will be:
- **Mes...
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