Introduction

1. What This Module Covers

This is the smallest module in the course: four patterns. It is also the hardest material. Every earlier lesson quietly relied on one guarantee. You have used it your whole career without noticing: the single-machine transaction.

On one database, "subtract from checking, add to savings" either fully happens or fully does not. The database's write-ahead log provides that all-or-nothing property. The word for it is atomicity. It works so smoothly that you have never had to think about it.