Backing up just the Transaction Log

The contents of this page apply only up to release 4.525/4.621, as the facility described has been removed in release 4.622. In release 4.622 you can use DYNABACK -SETSESSN -NODELETE to cause the transaction log to be restarted. The previous log file is renamed by changing the file extension from .log to.lbk, and you can use the utility of your choice to copy this file to another location if desired.

When backing up log files only, you must still occasionally make a complete backup of the database. One possible scheme is to make a complete backup once a week and a log-only backup each day. Then, should a database corruption occur, you can use the database restore utility:

• To restore the complete backup of the database
• To apply all the log files that are dated later than it
• To apply the log of the day

Restoring a database by applying log files is both a slow and unreliable process; one bad or incorrectly labelled log file disk can prevent the successful use of DBRESTOR.

1. On the DP4 System menu, select the Run program option.

2. Use this command to specify that only the transaction log is to be backed up:
   DBBACKUP −LOGONLY.

3. The Database Backup utility screen is displayed, and you are asked to enter the database name.

4. DP4 displays the current session number for the database, and prompts you to confirm that you have backed up the database using an alternative method:

   Has the database been successfully backed up? No

   Answer 'Yes' to continue with the backup operation. Answer 'No' to return to the DP4 System menu

   You are asked whether you want to verify the backup file. Answer 'Yes' to make DP4 check that the file is written to disk correctly. Answer 'No' to skip the backup verification.

5. Insert a diskette for the log file, as requested, and press <Enter>. DP4 begins copying the transaction log.

6. Once the transaction log is copied, you are prompted to label the disk with the current session number for the log. The Database Backup utility terminates and you are returned to the DP4 System Main menu.

   The log file will have been deleted from the database directory and the database and log session numbers incremented. A new log is started by carrying out a transaction on the database.