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Use

You can use log settings to configure the most important properties of transaction logging.

Table 1: Log Settings

Name

Description

Log mode

Specifies whether the database system supports software-based mirroring of the log volumes.

  • The log volumes are not mirrored

    Default value

  • The log volumes are mirrored (software-based)

    Only use this setting if hardware-based mirroring, for example using a RAID system, is not possible. Software-based mirroring reduces the performance of your database system..

    When software-based mirroring is activated, the database system writes redo log entries to two log areas in parallel (primary and secondary log area). The database system can only overwrite the log areas with new log entries after the log entries in the primary log area have been backed up.

Overwrite mode for the log area

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

  • OFF

    The database system can only overwrite the log area once the corresponding redo log entries have been backed up. We therefore recommend that you activate the automatic log backup function or regularly carry out interactive log backups.

  • 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 up to the time of the last data backup.

    Caution

    Switching on overwrite mode interrupts the backup history. If you have to restore the database after an error, no redo log entries are available for this period of time, and you lose all data since the last data backup.

If overwrite mode is on and you switch it off, you then have to carry out a complete data backup.

Redo log management

Specifies whether the database system writes redo log entries.

  • ON

    Default value

    The system writes redo log entries.

  • OFF

    Caution

    Do not switch redo log management off in normal database operation, because with restarting your database after a database crash, you lose all data since the last savepoint.

    Only consider switching redo log management off in special situations, for example in a test system or during a large load job.

If redo log management is off and you switch it back on, you then must carry out a complete data backup.
Note

In addition to the log settings, there are several database parameters that influence logging (see Database Parameters).

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