Build a scalable Recommendation Pipeline
Last updated: April 4, 2026
Quick Overview
Design a scalable recommendation system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Doordash
System Design
Software Engineer
Doordash
April 4, 2026Software Engineer
System Design Round
System Design
Medium
173
12
1,362 solved
Design a scalable recommendation system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Doordash 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
Failure handling and fault tolerance
Message queues and async processing
High-level architecture and component design
Monitoring, logging, and alerting
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 a region-wide outage?
- How do you ensure data consistency across multiple services?
- How would you handle a 10x increase in traffic overnight?
- How would you handle schema migrations with zero downtime?
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Requirements
Functional Requirements
- User Personalization: The system should provide personalized restaurant and food recommendations based on user preferences, past orders, and ratings.
- **Real-time ...
Capacity Estimation
Back-of-Envelope Calculations
- Daily Active Users (DAUs): Assume 10 million users.
- Requests per User: Assume an average of 5 recommendation requests per user per day.
- **Total Recommen...
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