AFAIK, MySQL and the like do not guarantee realtime responses, and network connections certainly do not. So if want something that is designed to do that, then use [pool], [textfile], or perhaps an embedded SQLlite, if it is quick enough.
By the way... although py/pyext might be hard to build compared to pdlua it can detach its execution from the pd thread and deliver late responses without halting the execution of pd.
gr~~~