Backup and Recovery › Recovery Procedures for Mixed-Mode Operations

Recovery Procedures for Mixed-Mode Operations

What is a Mixed-Mode Operation?

When database areas have been updated both in local mode and under the central version (for example, when an area has been varied offline, subsequently updated by a local transaction that used journaling, and then varied back online), the database must be restored by using both the local and the central version journals.

Mixed Mode Recovery

The following scenario is an example of synchronizing the recovery operations by explicitly using both the central version and local journals to ensure proper recovery of all database areas:

6 a.m.        Nightly backups taken

8 a.m.        System startup:  AREA1, AREA2,
              AREA3 are readied in update
              mode under the central version.

10:30 a.m.    AREA1 is varied offline.
              While offline, a local mode program
              (using a tape journal) updates
              AREA1 while the central version
              continues to update AREA2 and
              AREA3.

11:30 a.m.    A VARY JOURNAL command is issued
              for the central version journal.
              AREA1 is varied back online and
              the central version continues to
              update AREA1, AREA2, and AREA3.

12:00 p.m.    Database file I/O error occurs
              on AREA1.

When the database file I/O error occurs, the affected file associated with AREA1 must be restored by using both the local and central version journals.

Steps to Recover the Database

The following steps illustrate one approach to recovery, given the situation outlined above. Note that with this approach two separate rollforward operations are used. To process journal images from both central version and local mode operations in a single execution of the ROLLFORWARD utility, you must use the alternate recovery approach described next.

For a complete description of the recovery process, see 21.7, “Recovery Recovery Procedures from Database File I/O Errors".

An Alternate Approach

The following steps illustrate an alternate approach to recovery in a mixed-mode environment. With this approach, the local mode journal file is first merged with the archive files produced by the central version and the merged output file is used to recover the database in a single rollforward operation.

For a complete description of the recovery process, see 21.7, "Recovery Procedures from Database File I/O Errors".