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

Chapter 7 353
Logging and Recovery
Roll-Back Recovery
When transaction T4 is aborted, TurboIMAGE/XL completes the transaction by issuing an
abnormal end (DBABEND). This transaction is then seen as completed by the roll-back
feature and is not normally rolled back. If the aborted transaction is also to be rolled back,
the following DBRECOV command must be issued before issuing the DBRECOV >RUN
command (refer to the discussion of DBRECOV in chapter 8):
>CONTROL NOABORTS
The above command string causes the aborted transaction to be treated as an incomplete
transaction during roll-back recovery. When
>CONTROL NOABORTS is used, recovery must be
performed at system startup time before anyone modifies the database. Refer to "Record
Numbers" under the DBRECOV >CONTROL discussion in chapter 8 for considerations when
using the >CONTROL command.
Enabling the Roll-Back Feature
To enable the roll-back feature complete the following sequence:
1. Set the logid and build a log file (if logging to disk) as shown in steps 2 through 6 of
"Logging Preparation" earlier in this chapter.
2. For each particular database, disable access and enable the roll-back and recovery
features by entering the following DBUTIL commands. You can also enable the
MUSTRECOVER option if you wish to use it.
>>DISABLE database name FOR ACCESS
>>ENABLE database name FOR ROLLBACK,RECOVERY
>>ENABLE database name FOR MUSTRECOVER
Enable any other appropriate flags as discussed in step 7 under "Logging Preparation."
If the logid was not set and/or the log file was not built before the >>ENABLE command is
issued for roll-back recovery, a warning message that the logid or the log file is
non-existent is displayed on the screen. Enable any other appropriate flags as discussed
in step 7 under "Logging Preparation." Enabling for roll-back or MUSTRECOVER
automatically enables the database for logging.
3. Make a backup copy of the database as discussed in step 8 under "Logging
Preparation." You may use DBSTORE or TurboSTORE/iX 7x24 True-Online Backup
(with ONLINE=START or ONLINE=END option) regardless of the database being
open or closed with roll-back recovery.
4. Start the logging process and enable user access to the appropriate databases as shown
in "Logging Maintenance," earlier in this chapter. After the logid has been set and the
log file built, DBUTIL automatically enables logging when roll-back is enabled. Note
that ILR is not needed for roll-back recovery; however, if ILR is enabled together with
roll-back recovery, logging and ILR must be disabled separately.
When roll-back recovery is enabled, DBUTIL sets a roll-back flag in the root file to indicate
that roll-back recovery is enabled for the database. DBUTIL also reserves six words in the
root file for the roll-back time stamp (three words for the previous time stamp and three