If the processing is being handled by a program you wrote and are in control of, you could add an event that gets raised during each pass. That way your progress bar can receive the event and update.... 154 of 12,000 .....
But if the process is all contained in the MySQL database... I don't know what to tell you. Processing is happening inside a closed system.
this as its a series of update sql statements
I recomend incrementing the bar by "task" and not by time.
If you are in control of the series of SQL statements (each statement comes from your program, then Plater's suggestion makes the most sense.... Step 1 of 5....