Thanks all for your answers. > Keeping a document that contains a list of users subscriptions seems better > than a document containing all of a user's followers, particularly with the > end-user update models. However, I'd think either list can get large, which > is expensive when that document is updated. If users have lots of things > they follow, and that list is updated frequently, then it's still expensive. > I'd consider creating a separate document for each "subscription", a mapping > of a user following another user. >
Indeed, the list of followers can get relatively big especially if the user could follow things other than users such as groups, forums, posts, projects etc so the user doc could get pretty big and even if the user doesn't update very often the list of stuff he/she follows, it would be expensive to do so when it happens.
