How to: Transactions
A transaction is a series of database operations that are considered to be a _"single unit of work"_. The operations in a transaction either all succeed, or they all fail. In this way, the notion of a transaction supports data integrity when part of a system fails. Not all databases choose to support ACID transactions, usually because they are prioritizing other optimizations that are hard or theoretically impossible to implement together.

_Usually, relational databases support ACID transactions, and non-relational databases don't (there are exceptions)._