Don't bother trying to find Google's IPs, just block writing to the database when the UserAgent is GoogleBot. It happens more than once per page, as the AdSens

Don't bother trying to find Google's IPs, just block writing to the database when the UserAgent is GoogleBot. It happens more than once per page, as the AdSense bot will occasionally reread the page to see if its content changed and it should start serving different ads.