It’s common for programmer’s to cache data in order to improve performance. Constantly reading data from a database or file can be very resource intensive and can significantly slow down a website. I need to remember however that there is no guarantees on what will stay in the cache and what will be pushed out. Obviously I never use the cache to hold data which is not saved in a permanent location, otherwise when the memory fills up that data may be lost forever, but often I see code like this: