What Is Transaction Processing?

A transaction is unit of work consisting of one or more requests or updates to a system. A transaction is successfully completed with a commit command that finalizes all changes. If the transaction is not successful, a rollback command is used to undo changes and return the system to its previous state. A transaction, therefore, processes either all or none of its changes.

Consider, for example, the common transaction of withdrawing money from a checking account. The customer enters the request at an automated teller, causing a program to check the availability of funds, dispense the money, and update the balance of the user account. Each step must be completed before a successful transaction can occur.

Transaction processing software keeps track of each part of the transaction, ensuring data integrity by verifying that the transaction has been successfully completed before performing any updates.

The four basic properties of a transaction are known as the ACID properties:

• Atomicity – A transaction as a whole is either done or undone. If a transaction involves more than one discrete piece of information, all pieces are committed or none are.
• Consistency – A transaction leaves the data in a valid state. Either a change has been committed and the data has a new valid state, or no change occurs and the data returns to its previous valid state.
• Isolation – Each transaction occurs independently of other transactions taking place in the same environment.
• Durability – The effects of a transaction are permanent, so that even in the event of a system failure, upon restart, the data is available in its correct state.