[Doordash] [May 2026] Staff SWE Phone Screen: Design Instagram

Location: San Francisco, CA
Round type: Phone Screen
Question type: System Design

Interview Summary

This was an earlier DoorDash interview experience. The recruiter was very responsive and scheduled the interview quickly. The surprising part was that the first technical round was already a system design interview. The question itself was basic at first, but the deep dive went heavily into database design and scalability details.

Interview Details

• System Design Question — Design Instagram: The prompt was to design Instagram. The main focus was not just the basic posting and feed system, but how to handle the case where a celebrity publishes a post and a huge number of followers need to see it.
  • Celebrity Posting Focus: The key challenge was fanout. For normal users, a push-based feed model can work: when someone posts, the system pushes that post into followers’ feeds. For celebrity users, this becomes expensive because one post may need to reach millions of followers. A better design would likely combine push and pull models: push for normal users, but use pull or hybrid feed generation for celebrity accounts.
  • Database Deep Dive: The interviewer asked many detailed database questions. The discussion likely involved how to model users, followers, posts, feeds, likes, and comments; how to index feeds; how to handle high write volume; how to shard data; and how to keep feed reads fast under heavy traffic.

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