These three programs work in concert to provide the three basic functions needed to implement transactional recovery:

Resource locking

This function provides serialized access to changed resources.

Resource recovery logging

This function enables a resource manager to keep a record of the changes made to recoverable resources by a transaction.

Two-phase commit processing

This function provides the services that ensure that a transaction appears as an atomic operation. A two-phase commit protocol and backout processing work together to ensure that either all changes that are made by a transaction are committed, or that all of the changes are backed out.