AJAX + PHP Simple Example Script

I have a php script its purpose is to select a product in my database at random, and then process the results, the script then moves on to another product in the database and so on until all the records have been completed for that day. Because there is a lot of records in the database, i am using META REFRESH as below. very crude i know. Instead i want to use AJAX to run the script for me, as i think this will make the process cleaner, so i need ajax to call the script, and keep doing so until there is no more records left. However i also need ajax to recognise if my script has timed out, and if so reload the script