What is a database transaction?

A transaction groups several operations into one whole: either we commit all the changes or we roll them back. An example is a transfer: we take money from one account and add it to another. We don't want to save only half of that operation.

Transactions also have rules about how they see concurrent changes. That's called the isolation level. Wrapping code in a transaction doesn't fix every case where two requests try to take the last free spot. You have to choose the right way of writing or locking. A local PostgreSQL transaction doesn't automatically cover a call to an external API.

Drizzle is a library that helps describe tables and write queries from TypeScript. It's an example of an ORM, i.e. a layer connecting program structures to a relational database. It isn't the database itself and doesn't replace understanding transactions — you still have to choose which operations belong in one.