What is a transaction?

Question

When reading Spring tutorials I'm quite often coming across the @Transactional annotation.

When I google it, I get documentation that says things like:

Comprehensive transaction support is among the most compelling reasons to use the Spring Framework. The Spring Framework provides a consistent abstraction for transaction management that delivers the following benefits:

or:

A transaction manager is the part of an application that is responsible for coordinating transactions across one or more resources. In the Spring framework, the transaction manager is effectively the root of the transaction system. Hence, if you want to enable transactions on a component in Spring, you typically create a transaction manager bean and pass it to the component.

I have no idea what they're referring to here.

Can someone explain?

Answer 1

In its broadest sense, a "transaction" is a group of actions that should be performed as if they were a single "bulk" action. The term is most often used in the context of databases, but it can be applied to many kinds of programs (particularly ones that implement a command pattern). When we're talking about databases, and often even if we aren't, we want transactions to have the so-called ACID properties:

• Atomicity - The transaction is a single, unbreakable unit. It cannot be partially applied, or partially undone. It is either completely done, or not done at all.

• Consistency - The application/database/whatever must be in a valid state both before and after the transaction. If attempting to execute a transaction results in an invalid state, then we must "rollback" to the last valid state.

• Isolation - Every transaction is separate from every other transaction. No two transactions can ever "interleave". They are always executed one at a time (or in a way that is indistinguishable from "one at a time").

• Durability - Once the transaction has been executed, it stays executed forever. This one is mostly relevant for databases, where it means the change in data has actually been committed to disk, so that the new data cannot be lost even if the machine suddenly reboots.

Not all kinds of transactions need to have all four properties, but usually when the word "transaction" is used in a programming context, that implies a system that enforces at least some if not all of them. I believe Spring is referring to database transactions and does claim to enforce all of these properties.

Answer 2

A transaction is a set of actions related to each other in some way. Transaction is deemed complete when all actions have executed successfully.

One of main advantages of a transaction is ability to roll it back.

In development we have Command Pattern - commands are also transactions that can be executed, rolled back and queued.