TurboIMAGE/XL Database Management System Reference Manual MPE/iX V6.5 (30391-90011)

Chapter 7 329
Logging and Recovery
Logging Preparation
• Enable Rollback Flag. If you plan to use roll-back recovery, use the following
command to enable roll-back recovery:
>>ENABLE database name FOR ROLLBACK
After the logid is set and the log file has been built, the >>ENABLE command for
roll-back recovery shown above automatically enables logging for the database.
However, the >>DISABLE
database name FOR ROLLBACK command will not
automatically disable logging.
• Enable MUSTRECOVER Flag. When the MUSTRECOVER flag is enabled, only readers
can access the database after a system failure until the database is recovered. This
prevents modifications to a potentially inconsistent database.
>>ENABLE database name FOR MUSTRECOVER
After the logid is set and the log file has been built, logging is automatically enabled
when the ENABLE command is used to enable MUSTRECOVER. However, the >>DISABLE
database name FOR MUSTRECOVER command will not automatically disable logging.
• Disable Access Flag. By disabling the database for user access, you ensure that
modifications cannot be made to the database after restoring it. Any attempt to open
the database with a call to DBOPEN returns an error message. Access to the database
should be disabled before storing the backup copy, so that in the event of a system
failure the database is restored with access disabled. This prevents users from opening
the database and making modifications before recovery is executed. Disabling access to
the database is also useful as a general security measure to prevent database access at
unauthorized times. (Read the note below.) The DBUTIL command for disabling access is
shown below:
>>DISABLE database name FOR ACCESS
• Enable Recovery Flag. Enabling the database for recovery allows the
TurboIMAGE/XL recovery system to access the database. The database is stored with
recovery enabled so that when it is restored, it is ready for recovery. (Read the note
below.) The DBUTIL command for enabling roll-forward recovery is shown below:
>>ENABLE database name FOR RECOVERY
NOTE If you plan on using TurboSTORE/iX 7x24 True-Online Backup (with
ONLINE=START or ONLINE=END) when the database is open for access,
you will not be able to set the DISABLE FOR ACCESS or ENABLE FOR
RECOVERY flags for the backup copy. In the event recovery becomes
necessary, set these flags immediately after restoring the database from
backup.
The database can be stored with DBSTORE or TurboSTORE/iX 7x24 True-Online Backup