Thanks for the illustration. But if Uber team was using ORM, then expect ORM to take care of the pool of connections.

get data for receipt would be a SELECT and only write success to database would do INSERT or UPDATE. I expect junior programmer to complete the above in at least two SQL calls. I have a feeling they were trying something smart.

EDIT: hmm reading the other commenter above, probably they are trying to lock on the data for full data integrity. Okay. That makes sense then. I was looking at the problem from the wrong angle.