114005 Data extraction script

I need help with a script that will monitor job listings on a site, insert the new ones and remove those no longer available. The script will run automatically using a cron job and must be able to pick up where it left off if it runs out of memory. I have a basic web hosting account at the moment. I have the basic coding done (extracting job title, desc, etc.). Let me know your experience in data extraction, use of threads, etc. Thank you.