Ive been programing a C++ game/server for the past year. I have been using MYSQL for character logins, items, monsters, etc, etc. (im on windows). My question is, what are some of the databases that some big time developers use. IE. Battle.net, Diablo II, Diablo III, mythos, hellgate , etc, etc, etc. Do they have their own database they built? Or do they use an existing framework for logins, and character transfers.

I do know that in diablo II, they use character files to to transfer characters into the game world. But what about the login into battle.net.

Would it be wiser for me to stick with MYSQL, or is there something out there faster and more stable, or should I create a login type of system that looks through a file to see if you provided the correct password.

Can't wait to get some replies. Thanks!

PS. Currently the framework is much like battle.net, where you login into a lobby, create, and join games. The game server/lobby server are different servers too. So im just wondering about the lobby server for logins because I'm expecting several hundred thousand connections/logins.