When a change is made to a file and you are using journals, the system records the change in a journal receiver and writes the receiver to auxiliary storage before it is recorded in the file. Therefore, the journal receiver always has the latest database information.
Journal entries record activity for a specific record or for the file as a whole. Each entry includes bytes of control information that identify the source of the activity (such as user, job, program, time, and date). For changes that affect a single record, record images are included after the control information. The record image before the change can also be included. You can control whether to create a journal both before and after record images or just after record images by specifying the IMAGES parameter on the Start Journal Physical File (STRJRNPF) command.
All journaled database files are automatically synchronized with the journal when the system is started (IPL time). If the system session ends abnormally, some database changes might be in the journal, but some of these changes might not be reflected in the database files. If that is the case, the system automatically updates the database files from the journal.
Journals make saving database files an easier and faster task. For example, instead of saving an entire file every day, save the journal receiver that contains the changes to that file. You can still save the entire file on a weekly basis. This method can reduce the amount of time it takes to perform your daily save operations.