TurboIMAGE/XL Database Management System Reference Manual (30391-90012)

Chapter 7 377
Logging and Recovery
The Mirror Database
If some of the databases are not found, DBRECOV prompts for confirmation to purge the
RESTART file:
Can't re-open DATABASE basename .
CONTINUE WITH PURGE (N/Y)?
DBRECOV allows you to make sure that you wish to purge this recovery process. If not all
databases are in the RESTART file, this could be a different set of databases. Respond Y or
YES to purge the RESTART file, or N, NO, (or press carriage return) to stop.
Occasionally, DBRECOV can terminate abnormally due to a bad log file in the log set or a
system failure. If the user cannot RESTART recovery from the previous STOP point because
of a damaged or missing log file, PURGE the current RESTART file and begin the mirror
recovery process again. Listed below are the four basic steps used to reestablish the mirror
database system after an abnormal termination of DBRECOV:
1. Disable user access on the primary system and store the databases from the primary
system.
2. Purge the databases on the secondary system.
3. Restore the databases from the primary system onto the secondary system.
4. Start a new log set, enable user access on the primary system and start roll-forward
recovery on the secondary system.
Controlling the Logging Process
Backups on the secondary system are made more efficient by controlling the logging
processes on the primary system. Some important factors to consider before enabling
logging on the primary system follow:
• When logging to tape and to allow roll-back recovery, the database must be on the
system volume set. Logging to tape eliminates the step of storing log files with the
databases once they are rolled forward on the secondary system. However, keep track of
log file tapes that correspond with each database and RESTART file backup tapes.
Logging to tape requires a dedicated tape drive.
• When logging to disk and to allow roll-back recovery, the database and the user log file
must be on the same volume set. Logging to disk enables storing log files and the
databases on a single tape using an MPE/iX STORE command rather than a DBSTORE
command. When logging to disk, remember to backup all log files that were processed
after the last DBRECOV,RESTART along with the databases and RESTART file.
• When naming data sets, follow proper naming conventions. This will make storing the
databases, log files, and RESTART file much easier and eliminate the use of several
different tapes for the log files. If naming conventions are followed, an MPE/iX STORE
command using the "@" sign followed by the database name can be used to store the log
files, database, and RESTART file.
• When changing log files, either let the GETLOG AUTO option switch to the next log file
automatically and/or manually issue aCHANGELOG command to close the current log file
and open the next file in the log set.