What is the role of indexes in a PostgreSQL database and why are they needed?

Indexes in PostgreSQL are used to speed up searching and retrieving data from tables. They create a data structure (such as a B-tree) that allows quick access to the desired records without scanning the entire table. This is especially important when working with large volumes of data and complex queries. However, indexes occupy additional space and slow down insert, update, and delete operations, so they should be used thoughtfully.