Your laptop and your phone both edited the file. Who wins?

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Your laptop edits a file offline. Your phone edits the same file. The laptop reconnects. Whose edit survives?

Alice edits her thesis on her laptop, offline. She started from revision 7. Meanwhile her phone saves a different edit. That becomes revision 8. The laptop reconnects, and commits. Based on revision 7. The server checks. Current is 8, not 7. 409 Conflict.

That's the trick. Every commit says which version it edited. The check and the journal append happen in one transaction. No race.

Just overwrite? Then the phone's edit silently disappears. So keep both. The laptop saves its version alongside, as a conflicted copy. It syncs that as a new file. Then the user decides.

On every device, Alice sees thesis dot docx. The phone's edit. And right next to it, the laptop's conflicted copy. Two files. Nothing lost.

Many Dropbox users know this as a conflicted copy. Slightly messy. Never lossy. Two files beat one lost edit. Never silently throw work away.

Full breakdown in the lecture.