We have tools that show what queries are executed and the time it takes. But what next? What is going on there? Is it good that it’s doing that? Will some indexes help? In this talk, I will help you decipher database query plans and give some rules of thumb to understand if the database is doing the best it can. We will learn about different ways databases retrieve the data and how they estimate the cost of those operations. We will also use query plans to find the best function-based and partial indexes for different kinds of Django filter conditions. JSON fields? We will cover those as well! I will also share several anti-patterns I have seen in Django projects and show how to rewrite them in a database-friendly way.