MongoDB is a schema-less document database. Nonetheless, schema design is as important as ever, if not even more important. Why so?
Mostly, because the schema design in NoSQL is generally not determined by the data you want to store, but by the operations you want to perform. This is a fundamentally different approach. What I describe here works well for us, but it will almost certainly not work well for e.g. twitter, where the follower-count is probably distributed exponentially, rather than evenly.
Newsfeed BasicsOf course you know news feeds from facebook, linkedIn and many other software-as-a-service applications. The news feed's goal is to provide the user with relevant information that is usually roughly sorted by time, if not real-time.
The key to a good news feed is relevancy scoring (i.e., what does the user really care about?) which is often strongly, but not exclusively, based on recency and the relationship of reader and author. Recency does not only refer to the action that triggered the news item itself, but it might be the time the last comment was posted, or somebody interacted in any other way with the action item at hand.