The four key properties of transaction processing systems, the so called "ACID" properties are: Atomicity, Consistency, Isolation, and Durability. GT.M transaction processing provides the first three through the use of the TStart and TCommit commands. Durability is provided through the use of journaling.

Database systems, including GT.M, use journal files to provide recoverability of databases, thereby providing resiliency in the face of system hardware and software failures. Journaling uses journal files to record information pertaining to database updates.

Note that, journaling is not a substitute for good system configuration and design. For example, if a database and its journal files are on the same disk contoller, a hardware failure on that controller can damage both files, and prevent recoverability. The use of journaling therefore, complements other techniques to build a robust system.

Journaling requires no M programming. However, the M commands described later in this chapter may enhance the value of journaling.