"Every transaction in the database is applied in serial order, with a global lock ensuring that only one is being confirmed committed or aborted at a time." Is this true? I assumed you could transact in parallel, if there was no conflict, e.g. different tables were involved or maybe even different rows.
The confirmation for non-conflicting transaction is a very fast operation, it's not a bottleneck to protect it with a global lock. The whole process of writing the transaction is in parallel, you just have written data that might be discarded if the final commit fails. I don't think you can tell that two transactions do not conflict without holding a lock on the global state.
