DoorDash Infra Interview Experience and Key Design Insights

I had an interview for an Infrastructure position at DoorDash in early September. The interviewer was a European guy. The questions were unlike anything I'd seen in interview logs, but they were actua

I had an interview for an Infrastructure position at DoorDash in early September. The interviewer was a European guy. The questions were unlike anything I'd seen in interview logs, but they were actually quite easy. Coding Section: The question was to design a key-value cache to store words and check if a word exists.

Follow-up: If a prefix also counts,

return true. This part was basically implementing a simple cache + prefix check; nothing difficult, and I finished it smoothly. Design Section: After coding, we moved on to design. The interviewer asked: If the hard drive is large but the memory is small, and you can't fit all the content into memory, what should you do? My initial thought was to answer in the direction of prefix auto-complete: Store only the index in memory Then load the corresponding trie into memory as needed However, I felt I hadn't answered what he wanted to hear, and I failed in the end. Summary: The questions overall weren't difficult; they were fairly basic. The key was how to answer the design part in a way that closely matched the questions being asked. My mistake this time was not anticipating his focus; he probably wanted to hear me talk about storage tiering, indexing strategies, and the memory vs. disk trade-off. Hopefully, this will be helpful for those preparing for DoorDash Infra interviews.