Running php in background?

I wrote a php program that has to do a lot of processing on a couple large mySQL tables that can take hours, so often the page will time out or kick back a cannot find server errir. But it seems by checking the DB that records are still being updated. IS it possible the job runs in background even though it fails to delive the final results in the browser? I don't need the final results, it just says when the job is completed. Ideally, I would like to run the job in the background anyway. Can that be done?