User Guide

SAP AG November 2002
Log Volume
A database instance [Page 132] has volumes [Page 153] in which the log writer [Page 46]
records all changes to the database contents. These volumes are called log volumes. All log
volumes form the log area [Page 142].
The log entries are needed to ensure that the database content can be restored if a media
device fails. To guarantee safe database operation, the writing of all log entries to the log area
should always be active. This ensures that the log area cannot be overwritten until the log
entries have been backed up.
Managing Log Volumes
You can configure one or more log volumes when you install a new database instance.
During database operation, you can add new log volumes. The number of log volumes is
limited by the database parameter MAXLOGVOLUMES [Page 86].
See:
Database Manager GUI: SAP DB 7.4, Section Managing Database Instances [See SAP DB
Library]
Database Manager CLI: SAP DB 7.4, Section Adding a Volume [See SAP DB Library]
Log Mode
Usually, the log mode [Page 143] should be set to SINGLE.
See:
Database Manager GUI: SAP DB 7.4, Section Changing the Log Mode [See SAP DB Library]
Database Manager CLI: SAP DB 7.4, Section Changing the Value of a Database Parameter
[See SAP DB Library]
For safety reasons, the log area should always be mirrored on a hardware basis. If it is not
possible to mirror the log area on a hardware basis, you can achieve a software-based
mirroring by setting the log mode DUAL.
Log Backups
• To ensure uninterrupted database operation, you must ensure that there is always
enough space available in the log area.
For safe database operation, it is necessary for the log entries to be backed up at regular
intervals (including for mirroring the log area).
•
Therefore, carry out log backups [Page
142] at regular intervals. You can best ensure
uninterrupted database operation by authorizing an automatic log backup [Page 126].
The log segment size, the size of the log volume, and the capacity of the backup medium
must be –matched to each other. The log segment size should be selected so that enough
space remains in the log area during the backup of a log segments to ensure that the
changes can also be incorporated.
Multiprocessor Configuration
To allow multiprocessor configurations to be used to the best advantage, the database
system supports external/internal tasking that can be configured.
User Manual: SAP DB 144