This article is part of our Faster Rails series. Check out the previous article about proper database indexing.
As the scope and size of a Rails project grows, actions that were blazingly fast can become slow, and even downright unacceptable. The cause behind this issue can be an exponential growth of your database tables that makes lookups and updates much slower. If this is the case, adding missing indexes to your database is a cheap and easy way to drastically improve the performance of your application.