1.1 Conceptual Overview

A transaction is an atomic unit of work (UOW) that can either succeed or fail. A transaction cannot be partially completed. Because a transaction can be made up of many steps, each step in the transaction has to succeed for the transaction to be successful. If any step of the transaction fails, the entire transaction fails. When a transaction fails, the system has to return to the state that it was in before the transaction was started. This process is called a rollback. When a transaction fails, the changes that had been made are said to be rolled back.

The following sections provide a conceptual overview of the major components and processes of the transaction processing services:

  • Transaction Trees (section 1.1.1)

  • Two-Phase Commit Protocol (section 1.1.2)

  • Phase Zero (section 1.1.3)

  • Single-Phase Commit (section 1.1.4)

  • Core and Optional Protocols (section 1.1.5)