Scale is always one of the most difficult things for me to plan for. Over last summer I was working on a registration system for an ISP which worked really well

Scale is always one of the most difficult things for me to plan for. Over last summer I was working on a registration system for an ISP which worked really well in testing. Once the database exploded to over 1M rows however, that application's performance was noticeably suffering. Unfortunately now that system is live, and the schema can't be changed for a few months...oops