我应该使用单独的表来存储在线用户，还是应该在extant members表中使用其他字段?

I'm working on an online system that allows users to interact socially and of course it will be important to be able to identify users that are in fact online. I know about HTTP being stateless and I know about using sessions, so I'll need to accomplish this by comparing the last active time of a user to an arbitrary expiration time. I'm working on an online system that allows use