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.