API Design · Middle · Question 19 of 75

Two clients edit the same document. How can an API prevent one from silently overwriting the other?

1Lock the resource for each client for an hour
✓Correct answer: Optimistic concurrency: clients send If-Match: <etag>; if the resource changed, the server answers 412 Precondition Failed
3Let the last write win always

Explanation

The client then reloads, merges or asks the user. 428 Precondition Required can force clients to send If-Match.

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