User's Manual

23 Database Backup 88
7signal Ltd, Panuntie 6, FI-00620 HELSINKI, FINLAND, [phone], [e-mail], www.7signal.com
7signal Sapphire Carat Carat User Guide Release 3.1
Example:
# 7db backup now /mnt/backups offline
Archival logging
Sapphire processes will not be stopped during backup process.
Example:
# 7db backup now /mnt/backups online
23.2 Database logging
In short, the logs of a database system are the most precious. It is justified to say that the logs
are the database as they are written first and the tables are updated after that.
IBM DB2 provides alternative logging methods that affect the backup options. So called
'circular logging' method keeps the size of the logs very predictable. The other option used in
7signal Sapphire is so called 'infinite archive logging'. This is very flexible a logging method
provided that there is a special file system available. Practically the file system must not fill up
ever.
The default logging method in 7signal Sapphire is 'circular logging'.
23.2.1 Purging database logs
Circular logging
There is no need for purging in case of circular logging. The default logging method in 7signal
Sapphire is 'circular logging'.
Infinite archice logging
There is one secure way of purging the log files in the infinite archive directory. Offline backup
has to be done and this comes with price of the 7signal Sapphire halt. Offline backup provides
one single and unique point-in-time to be restored later. Once the offline backup exists, the
log files in the infinite archive directory become obsolete and may be removed.
The other option comes with no warranty whatsoever. The option is to keep 7signal Sapphire
running and to delete log files in the infinite archive directory. To understand what files are
likely to be unused, the active log files has to be followed to see the time to fill up a single log
file and then deduce what infinite archive files might be available for deleting . If one chooses
this option, setting the safety margins reasonably high is advisable.
In case there is both a system crash and a log file has been deleted too early, the
recovery shall never be able to finish. In this case, the only consistent system
stage is available at offline backup time.