Things always go wrong, because DBs still run on fallible hardware, operating systems and networks.

• Examples

What is a transaction?

A mechanism for simplifying this issue:

• Group multiple operations (reads/writes) on multiple objects into one unit of execution →
• Either the entire transaction succeeds (commit) or it fails (abort, rollback).

The application is free to ignore potential error scenarios and concurrency issues, because the DB takes care of them instead (called safety guarantees).

Weaker guarantees

Some apps can benefit from weakening transaction guarantees or abandoning them entirely for performance or higher availability reasons [this, this].

• Table of contents

The Meaning of ACID

Atomicity, Consistency, Isolation, Durability:

• A term to describe fault-tolerance mechanisms in DBs.
• However, each DB implementation of ACID is different from one another; it’s become mostly a marketing term.
• Systems that aren’t ACID are sometimes called BASE = Basically Available, Soft state, and Eventual consistency