How does the use of indexes affect the speed of SQL query execution and overall database performance?

The index structure in a database is usually based on a data structure called a B-tree (or its variations, such as B+-tree).

A B-tree is a balanced search tree that supports insert, delete, and search operations efficiently in logarithmic time. It is optimized for working with large data volumes on disk, minimizing disk access.

Indexes based on B-trees allow quick record retrieval by key, significantly speeding up query execution.