What are the disadvantages of database indexes?

This post details the disadvantages of excessive secondary database indexes, specifically increased storage consumption and slower write operations (inserts, updates, deletes). It provides SQL queries to identify unused indexes based on cardinality and explains how to use MySQL's invisible indexes feature to test the impact of dropping an index before permanent removal. It also highlights PlanetScale's `Insights` feature for performance testing and its deploy request process for safe schema changes.