Design Gmail
Last updated: December 21, 2025
Quick Overview
Design the architecture for Gmail. Cover scalability, data storage, caching, and real-time requirements.
Google
System Design
Software Engineer
Software Engineer
Onsite
System Design
Medium
28
12
751 solved
Design the architecture for Gmail. Cover scalability, data storage, caching, and real-time requirements.
System design interviews at Google 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
Database selection and data modeling
Monitoring, logging, and alerting
Failure handling and fault tolerance
Load balancing and horizontal scaling
High-level architecture and component design
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
- What would the deployment pipeline look like for this system?
- How would you handle a 10x increase in traffic overnight?
- How would you implement rate limiting to protect the system?
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Requirements
Functional Requirements
- User Registration and Authentication: Allow users to create accounts, log in, and recover passwords.
- Email Sending and Receiving: Users must be able to send e...
Capacity Estimation
Back-of-Envelope Calculations
- User Base: Assume 1 billion users. If 50% are active daily, that’s 500 million users.
- Email Volume: If each user sends/receives an average of 20 emails ...
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