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Procedure documentationConfiguring Database Transaction Logging Locate this document in the navigation structure

 

The database system logs all database transactions that change application data or the database catalog. It writes information about these changes into log entries. If necessary, the system can later use these log entries to roll back or repeat SQL statements.

Procedure

Use one of the following database tools:

Database Studio, Database Manager CLI, or CCMS (in SAP systems only)

Changing Log Settings

The log settings specify the most important logging properties.

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.

Log partitioning

To increase the speed with which the system writes log entries to the log area, you can divide the log area into several log partitions. The system can then write log entries to several log partitions in parallel.

A log partition consists of one or several log volumes and, if applicable, the respective mirrored log volumes (if you have enabled software-based mirroring of the log area). When you create a log volume, you assign it to a log partition. If you do not assign the log volume to a partition, the system automatically assigns it to the first log partition.

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 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.

    End of the caution.

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 Caution

    Do not switch redo log management off in normal database operation. When redo management is switched off, the system does not write regular savepoints. This means that if you restart your database after a database crash, you lose all data since the last savepoint. If you have to restore your database, you can only restore it to the state of the last data backup.

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

    End of the caution.

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

More information:

Changing Log-Related Database Parameters

To specify further logging properties, for example the log segment size or the number of log volumes, use database parameters (see Database Parameters).

Increasing the Size of the Log Area

Log entries are stored in the log area. If you need to increase the size of the log area, add log volumes.

Note that when the log area is full, you first need to carry out a log backup.

Caution Caution

Adding a new log volume will not immediately reduce the filling level of the log area. The system will only use the new log volume after you have carried out a log backup.

End of the caution.

More information:

More Information

Concepts of the Database System, How Databases Log Data Changes