I might be wrong, but you probably didn't handle as much traffic as Github does. Bugs and outages probability is a asymptotic to normalized traffic. At least intuitively.

No we didn't luckily but we also didn't have that much money. Biggest problem was 50k+ people trying to reserve a limited amount of stuff at the same time and 5k+ logins/second (at first we made the mistake to write last_login to MySQL ;-)

We changed to a write behind setup (e.g. with Redis PubSub or any other queue). I think everyone with some experience will use async write behind and not sync writes during a request as we did.

How did you go about saving login/device data? We are going to do this soon in our app and I'm looking for good use cases and solutions