I am baffled any time I’m on facebook how horrid it is. Loads insanely slowly, won’t accept picture uploads at random, randomly doesn’t let you share to people in your friends group (it will just hide people for no reason). Such a terrible website. Sadly I have to stay on it for friends and music reasons (there is nothing else anyone I know uses) but man, it’s crazy how badly they want you to install their spyware app so you don’t use the browser version.
I used to work at FB a a while back (working on infra, not FE or anything user touching) and we would have private development servers and occasionally I would need to do work on the FE PHP repo (called www) and would need to stay a development server for FB.
It would connect ti the various services and database as read only and was a private copy. It functioned just like a real webswver with the exception that the cache was stone cold. It would takes MINUTES to load the front page the first time. It is crazy how much caching just makes it functional.
The problem is that there are so many services and datasets read all the time.