Database logging
Database logging is an important part of your highly available database
solution design because database logs make it possible to recover from a failure, and they make it
possible to synchronize primary and secondary databases.
All databases have logs
associated with them. These logs keep records of database changes. If a database needs to be
restored to a point beyond the last full, offline backup, logs are required to roll the data forward
to the point of failure.
Two types of database logging are supported: circular and archive. Each provides a different level of recovery capability:
The advantage of choosing archive logging is that rollforward recovery can use both archived logs and active logs to restore a database either to the end of the logs, or to a specific point in time. The archived log files can be used to recover changes made after the backup was taken. This is different from circular logging where you can only recover to the time of the backup, and all changes made after that are lost.