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

Chapter 7 363
Logging and Recovery
Post-Recovery Options
Post-Recovery Options
After a recovery has completed, there are three procedural options. The option chosen
determines the recovery procedure in the event of a subsequent system failure. Together,
the database administrator and system manager or console operator should agree upon
the best post-recovery procedure to avoid confusion at recovery time. The options available
after recovery include:
1. Making a new database backup copy and starting a new log file from the console with
the CHANGELOG command.
If you use TurboSTORE/iX 7x24 True-Online Backup (with ONLINE=START or
ONLINE=END option), you can start a new log cycle, or restart with the same log file.
In the event of a subsequent system failure, the new database backup copy is restored
and recovered against the new log file. This option allows for a straightforward recovery
procedure but delays users from accessing the database until the new backup copy has
been generated.
2. Resuming transaction logging to the same log file using the RESTART option without
creating a new backup copy.
In the event of a subsequent system failure, the old database copy is restored and
recovered against the log file. This procedure is the same as the original recovery, but
takes longer due to the additional log file records. Users can access the database after
the first system failure without waiting for it to be stored.
3. Initiating logging to a new log file without creating a new backup copy.
In the event of a system failure, the old database copy is restored and two recoveries are
executed: the first using the old log file and the second using the new log file. This
procedure is not recommended if option 2 is available.
Until a new database backup copy is generated, if you consistently start logging to a
new log file after a system failure, a total recovery preceded by n failures requires n
executions of the recovery system.
The second and subsequent recoveries of a database against more than one log file are
not permitted unless the DBSTORE flag is disabled. This is because the first modification
executed again from the first log file clears the DBSTORE flag from the database root file.
Subsequent calls to DBRECOV can only succeed by specifying the >CONTROL NOSTORE
option. Ensure that the log files are recovered in the proper consecutive order.
NOTE For options 2 and 3, do not restart a log file before the database has been
recovered after a system failure because of the following reasons:
• Some log records could have been lost in the system failure, and
• The log file may not be consistent with the true state of the database.
A recovery is necessary to bring the database and log file into agreement
before restarting the log process.