How to deal with many page/post revisions at multisite websites


I did notice that a multisite project can store a lot of page/post revisions in wp database (as well as disk space and speed issues later).

How WP deals with that? All post revisions is kept forever on database, or just recent ones?

If it is not managed by default, there is some plugin to limit revisions (compatible with multisite), let's say keeping only 4 or 5 latest revisions?

I'm curious about how a project like edublogs deals with that... if nothing is done, I do imagine thousands of users with million posts and (maybe) billions of revisions all stored on database...