Our new user_outbound_follows table allows us to efficiently find out who a user follows; since the partition key is the username of the following user, we'll only be accessing a single partition to answer the question. It does not, however, provide any way to find out who follows a certain user. In order to broadcast users' status updates to their followers, we'll certainly need to be able to find out who their followers are.
To accomplish this, we'll create a new table, which is the mirror image of user_outbound_follows:
CREATE TABLE "user_inbound_follows" ( "followed_username" text, "follower_username" text, PRIMARY KEY ("followed_username", "follower_username") );
The new user_inbound_follows table looks exactly like ...
