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 Log Volumes and Log Area 

The volumes in which all changes to database content are recorded as log entries are called log volumes. Together, all log volumes form the log area.

Log entries are needed alongside data backups to guarantee that the database instance can be recovered after errors, either to its last consistent state, or to any other state in the past. When you recover the database instance, the log entries that are still in the log area are restored. If the required log entries no longer exist, then the corresponding log backups are restored.

Importance of Log Backups

The log area is overwritten cyclically. However, if you use standard log backups, the existing log entries in the log area can only be overwritten after they have been backed up. If no new log entries can be written, then the database crashes. For this reason, you must back up the log area at regular intervals, for example, with automatic log backups.

You can use the Database Manager GUI to monitor the fill level of the log area (see Displaying Log Area Information). If the log area is full, make a log backup so that the log area can be overwritten again.

For security reasons, we recommend that you mirror the log area. If hardware-based mirroring is not possible, you can use an appropriate log mode setting.

See also:

Log Settings

In log backups, the log area is not saved as a whole. Instead, it is saved in backup units, called log segments. You must match the size of the log segments, the size of the log volume, and the capacity of the backup media to each other.

For more detailed information about logging, see Background Knowledge.

 

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