- 5 more design problems: news feed, chat/messaging system, video streaming (YouTube), Google Drive/Dropbox, distributed job scheduler.
- Read Spanner and GFS papers (skim, focus on the tradeoffs and why they were made).
- Deep-dive drills: pick 3 designs you’ve already done and go one level deeper on a single component (the sharding scheme, the hot-key problem, the consistency guarantee). L5 interviews live in these deep dives.
- Behavioral: rehearse all 10 stories out loud, recorded. Cut every one to ≤ 2.5 min. Prepare 3 sharp questions for your interviewers.
- Coding maintenance: 8 problems.
- Second mock: full system design round with a human.
Exit criteria: no story runs long, no story is missing a measurable outcome, and every story answers “what would you do differently?”