Forward recovery can be used to take an older version of a table and apply the changes logged on the journal to the table. Backward recovery can be used to remove changes logged on the journal from the table. When an SQL schema is created, a journal and journal receiver are created in the schema. However, because placing journal receivers on their own ASPs can improve performance, the person managing the journal might want to create all future journal receivers on a separate ASP.
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When a file is being journaled, activity such as file-opens, file-closes and data updates are recorded. The journal receiver is where the journal entries are actually recorded.
The journal "connects" the receiver to the file. Also, you should put journal receivers in the same library as the file. Create a journal. Although you can journal multiple files to the same journal and, in some cases, that is actually preferable , you will generally want to have a journal "serving" a single file.
Start journaling the file. This is how you associate a file to a journal. Once the association is made, the system will record in the journal receiver a copy of any record added, updated or deleted from the file. Other activity, such as when the file is opened and closed, can also be recorded in the journal receiver if you choose by selecting the appropriate options on the STRJRNPF command. PR, NR for journal entry J. Journal and journal receiver operations J. These include such things as references to the previous receiver PR or the next receiver NR in a chain.
Also, at IPL-time, an entry is made e. File operations F. This category includes file opens OP and file closes CL. Record operations R. Commitment control C. Anything related to commitment control falls into this category. CMPJRNIMG: This command compares and lists the difference between the before-image and after-image of a record, or between the current after-image of a record and the previous after-image of the record. DSPJRN: This command displays or prints the journal entries that are in the journal receivers associated with the specified journal.
This command has outfile support so you can list the journal entries to a database output file for further processing or analysis. RCVJRNE: This command allows a specified user program to continuously receive journal entries one at a time as they are written to the journal. The behavior is similar to an exit program. RMVJRNCHG: Use this command to remove changes that have occurred to a database file from a specified point in time to some previous point in time allowed only if before-images were recorded during the time.
WRKJRN: This command displays a menu from which you can perform many journal-related functions, such as system-assisted recovery of journaled files.
Principle of Journals and Journaling on the AS/400
How to Implement Journaling on AS/400 files?