- High Scalability

Im sure most are familiar with Facebooks 'news feed'. If not, the 'news feed' basically lists recent activity of all of your friends.

I dont see how you can get this information efficiently from a DB:

* Im assuming all user activity is inserted in a "actions" table.
* first get a list of all your friends
* then query the actions table to return recent activity where the activity belongs to someone on your friends list

This can't be efficient especially considering some people have 200+ friends.

So what am I missing? How do you think Facebook is implementing their "news feed".
Im not asking for any specific details, just a general point in the right direction, as I cant see how they are implementing the 'news feed efficiently.
Thanks.