Performing a dummy backup is potentially very dangerous, as if the database has an undetected corruption, and you choose to delete the log file, you will have no reliable way to ensure the transactions contained in the log file are not lost.
As of release 4.621, there are few, if any, DP4 utilities that will cause a backup to be forced without very good reason.
You may want to perform a dummy backup in either of these circumstances:
You are backing up the database using other utilities and you want to increment the database and log file session numbers and delete the log.
You have been or will be prompted by the system to do a backup, but you do not wish to do one. (Performing a dummy backup in this situation is only really acceptable in a development environment, and where the data is non critical.)
The dummy backup utility performs no database checks at all. So, if using the operating system to back up your system to, for example, a tape streamer, run an integrity check as well. (Note that the standard DP4 backup utility does a partial integrity check when you use the -TAPE command tail.)
Two different utilities can perform a dummy backup:
DYNABACK -SETSESSN can perform a dummy backup while the database is in use.
SETSESSN is the original dummy backup utility. It requires exclusive access to the database. It also has some special command tails that can modify its operation.
To perform a dummy backup:
On the Database Backup, Recovery & Check menu, select the Dummy backup option. Prior to release 4.621 this option invokes SETSESSN. From 4.621 it invokes DYNABACK −SETSESSN.
Select the database.
You are asked whether you wish to delete the transaction log file. Answer 'Yes' to delete it. Answer 'No' to keep the log.
The database session number has been incremented. If there was a log file, the log file session number for new transactions has been incremented. If you are using SETSESSN this causes a problem where you did not choose to delete the log file, in that you are prevented from updating the database until you have manually renamed or deleted the log file. This problem does not arise when you use DYNABACK -SETSESSN.
Several command tails exist to modify the dummy backup operation. For example, if the dummy backup is part of a batch process and you want to suppress output to the screen, you should run SETSESSN with the -SILENT command tail. All the SETSESSN command tails are described below:
|
Command Tail |
Description |
|
-DELETE |
Deletes the log file |
|
-NODELETE |
Retains the log file |
|
-SILENT |
Suppresses screen output |
|
-NOINCSEQ |
Does not increment the backup sequence number |
|
-DBCHECK |
Performs a dummy integrity check |
Alternatively, a dummy backup can be achieved with the dynamic backup utility as follows:
On the DP4 System menu, select the Run program option
Use this command to perform the dummy backup:
DYNABACK -SETSESSN [-DELETE|-NODELETE]
where -DELETE is optional and deletes the transaction log, and
-NODELETE is optional and renames the transaction log to
<DATABASE_NAME>.LBK
The database session number has been incremented. If there was a log file, the log file session number for new transactions has been incremented.