Software Engineer · Phone Screen · System Design

Roblox — Software Engineer ✅ Passed

Level: Mid-Level

Round: Phone Screen · Type: System Design · Difficulty: 7/10 · Duration: 60 min · Interviewer: Unfriendly

Topics: API Design, Idempotency, Correctness, Database Selection, Cache Design, Sharding

Location: San Francisco Bay Area

Interview date: 2026-02-15

Summary

I discussed the design of a like/dislike system, including API design, idempotency, correctness, database selection, cache key-value design, and sharding.

Details

I interviewed for a software engineer position and the technical phone screen focused on designing a like/dislike system. The system allows users to like or dislike items, view their status for each item, see past liked items, and view the exact like count for each item. The discussion covered the following aspects:

• API Design: Designing the APIs for liking, disliking, and retrieving item status.
• Idempotency: Ensuring that duplicate requests don't cause unintended side effects.
• Correctness: Handling like to dislike and dislike to like transitions correctly.
• Database Selection: Choosing an appropriate database for storing the data.
• Cache Key-Value Design: Designing the cache to improve performance.
• Sharding: Implementing sharding for scalability.

The interviewer expected me to actively drive the interview and perform a deep dive into each area.