The follower database is a feature that helps the scalability of your Heroku applications.

Through the follower database, Heroku provides a way to increase the efficiency of reading your database data by creating a master-slave structure. Each slave is one follower in read-only mode, and the data is updated from master to slave in real time.

The most common use of a follower database is when you want to increase the performance to access your data; for example, imagine that you have a web application with a huge number of users. If all users access the same database, you will probably have performance issues. A good solution to this is to create copies of your main database, and when each user needs any data, the system redirects the request for a copy of the database. This way, you have a database distributed system. Through Heroku Postgres follower databases, you can add many follower databases for your application.