Google Docs

How this question breaks down

1. 1Concurrent editsCore27 minLet two people type into the same sentence at the same moment and have every screen end up with the same text, without locking anyone out.
2. 2SessionsCore30 minGet everyone editing one document onto the same server, show who is there and where they are typing, and bring them back without losing a keystroke when a connection or a server drops.
3. 3HistoryCore25 minKeep every change to a document so anyone can see who wrote what, open any earlier version and restore it, without the log growing forever or reads getting slow.

Work through the parts in order and you’ve covered the full design. Each part is one topic.