Name

Description

Log mode

Defines whether the database system supports software-based mirroring.

●     Log area not mirrored: system default

●     Log area mirrored: Use this setting only if hardware-based mirroring is not possible. Software-based mirroring reduces the performance of your database system.

In software-based mirroring, the database system writes to two log areas in parallel (primary and secondary log area). The database system can only overwrite the log areas when the log entries in the primary log area have been backed up.

If there are problems accessing a log volume in the primary log area, the affected log volume is flagged as BAD, and the database instance is transferred to the OFFLINE operational state. To restore the defective log volume, replace the respective hard disk and, in the ADMIN operational state, copy the entire contents of the corresponding mirrored log volume to the primary log volume.

Overwrite mode for the log area

Defines whether the database system can overwrite redo log entries in the log area even if they have not been backed up

●     Overwrite mode off: system default

The database system can only overwrite the log area once the corresponding redo log entries have been backed up. To obtain a complete log backup history, you need to activate automatic log backup or regularly perform interactive backups.

●     Overwrite mode on:

The database system cyclically overwrites the log area without first backing up the redo log entries. This results in gaps in the backup history. This, in turn, means that you can only restore your database instance up to the time of the last data backup.

If overwrite mode was on and then you switch it off, you then have to execute a complete data backup.

Redo Log Management

Defines whether the database system writes redo log entries

●     Redo log management is switched on: System default

●     Redo log management off:

In rare cases, it may make sense to switch off redo log management, for example during a big load job. Note that this interrupts the log backup history. If you have to restore the database instance after an error, no redo log entries are available for this period of time.

If redo log management was switched off and then you switch it back on, you then have to perform a complete data backup.