Closed-book card for day 77. This file is the interviewer. It is not a worked example.
Do not open the Phase 4 lessons while this timer is running. Do not scroll past the attempt barrier on the day 77 page. This is not the social graph, ephemeral stories, web crawler, order book, feature flags, or audit log.
Design a large email inbox.
People receive and send email. They browse folders, open messages, search, and download attachments. Mailboxes can be very large. Ingest must not make listing the inbox slow.
You have 35 minutes. Blank page. No notes.