Define and explain the principle of Journals and Journaling on the AS/400 and the use of the relevant commands e.g. CRTJRN etc. How can I stop a program from journaling?
The OS/400 backup and recovery guide is an excellent place to begin your knowledge about journaling. This is really where you should start, but I'll give a quick overview. Journaling works on Physical files. The primary function of journaling is to store record level database changes and allow those changes to be "rolled back" or undone, if needed. When a file is journaled, any changes at the record level are recorded to the journal first and are then applied to the database record. This is not to say that journaling will always be able to undo any changes that you've done to a file, but it does provide reasonably good protection and a good audit trail. For instance, it will not be able to recover a from a clear physical file command. Journaling requires journal receivers and journals. Journal receivers hold the record level data and journals hold information about what files are journaled and how they are journaled. To start journaling you'll first have to create a journal receiver. Using the CRTJRNRCV command. Then you can create the journal with the CRTJRN command. To start journaling on a file, use the STRJRNPF command and to end it you will use the ENDJRNPF command. Other useful commands are WRKJRNA, DSPJRN, CHGJRN. Since journal receivers contain record level data from the files being journaled, they can use a lot of disk space so you will want to change, save and purge your old journal receivers on a regular basis.