In the DAO does a transaction return anything to inspect the results? For example if I update a record in a transaction, does it return any success/failure information or a result or will it only throw an exception if there's a failure to make the write? Similarly, for the DSL I see calling the Table.update returns an Int that looks like the number of rows actually updated? Does anything other than the expected number indicate a failure, or would those only be surfaced as exceptions?

failures usually lead to exceptions. I dont think I have experienced otherwise. ie. there are options like

insertIgnore

for fire-and-forget situations