Concurrent Updates and Lost Updates

If you have ever edited a shared document, you have encountered the possibility of someone else saving a change while you are still working. The same problem arises with a shared reading list: one editor changes its name while another updates its description. Both saves may succeed, yet the second can quietly restore the old name. Each request was valid, and neither was a duplicate, but the API still lost a user's work.

The service needs rules for handling updates whose editing or execution periods overlap.

This chapter explains lost updates, why narrower payloads and database transactions are not sufficient by themselves, and how to choose a conflict policy that fits the resource.