Roll Forward Technical Concepts

Method

The roll forward recovery process is used when the system goes down and object loss or damage makes it impossible to perform a rollback.  The process involves restoring the last backed up version of the data base to disk.  Any receivers that were backed up from the time of the last master file backup until the present should also be restored.  The Roll Forward program (RM300P) is then executed.

Processing

The Recovery Management Roll Forward Control program (RM300C) provides control for the roll forward recovery stream.  The stream flow is as follows:

1.   The Recovery Management Roll Forward Select Screen (RM300S01) is displayed.  This screen will accept the name of the starting journal receiver to be used in the roll forward process.  This screen is described in detail In the Program Descriptions section.

2.   The next step of the roll forward procedure is determined.

a.   If F3 (Exit) is pressed, then processing ends.

b.   If the ENTER key is pressed, then processing continues at step 3.

3.   Allowable roll forward entries are placed into the physical Journal File (RMJRNLP). All allowable entries, starting from the receiver entered on the select screen through the current receiver, are included.  The only entries that will be rolled forward are:  update (UP), delete (DL), add (PT), rollback (RC and UR), roll forward (AY), reorganize (RG), and clear (CR).

4.   Entries that may prevent a roll forward are placed into the Roll Forward Prevention File (RM300AP).  All entries that may prevent a roll forward, starting from the receiver entered on the select screen through the current receiver, are included.  The entries that may prevent a roll forward are:  clear (CR), end journaling (EJ), initialize (IZ), member delete (MD), member save with storage freed (MF), member moved (MM), member renamed (MN), member restored (MR), and reorganize (RG).  It should be noted that not all of the above entries will prevent the roll forward from continuing.

5.   The Recovery Management Roll Forward program (RM300P) is called.  This program is described in detail In the Program Descriptions section.  If no entry exists that will prevent the roll forward from continuing, then each entry in the Roll Forward Control File (RM300AP) is applied.  The Roll Forward Report (RM300) is printed by this program.  The Roll Forward Exception Report (RM301) is printed when necessary.

6.   The physical Journal File (RMJRNLP) is cleared, and processing ends.