What is the best way (in Rails/AR) to ensure writes to a database table are performed synchronously, one after another, one at a time?

You can lock a specific table (or tables) with the LOCK TABLES statement.

If you are worried/troubled about/with multiple processes writing to the 'same' rows - as in more users updating the same order_header row - I'd suggest you set some marker bound to the current_user. Id on the row once /order_headers/:id/edit was called, and removing it again, once the current_user releases the row either by updating or canceling the edit.

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