User's Guide

25 Database Backup 79
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7signal Sapphire Carat Carat User Guide Release 3.0
25 DATABASE BACKUP
It is possible to backup databases in 7signal Sapphire. Given a proper backup, the system state
may be recovered completely in case of system crash. There are two remarkably different
alternatives and an option not to backup the database. The default in 7signal Sapphire is no
backup. While this option is known to be non-optimal for any production environment, it is
chosen as default to force every organization to define their own backup policy.
25.1 Backup options
25.1.1 Automated backup with server downtime
Backup with downtime is a circadian backup based on Unix cron that pauses the
measurements by stopping the Carat server and closing the underlying database connections.
In quiescent mode a full backup of the database is made and stored to the desired location in
the Carat server file system. The user is responsible for managing the backup files, moving and
purging and so on. This type of logging is later referred as offline backup.
25.1.2 Automated backup without server downtime
Online backup is a circadian backup based on Unix cron that keeps 7signal Sapphire in
production while creating the backups. While this obviously is the most tempting option, it
comes with a price of heavier administration.
To understand the difference between the methods – thus making one able to decide on
appropriate backup policy – we must understand database logging methods first.
25.2 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'.
25.2.1 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'.