User Guide

SAP AG November 2002
Need for log backup
• In the case of a recovery, a data backup [Page 131] alone is not enough to restore the
current state of the database instance [Page 132] up to a certain point in time (for
example, the time just before the disk error occurred).
To restore the current state, both the data backup and the log entries that were written
after the data backup must be imported into the database system.
• If new log entries cannot be written because there is not enough storage space in the
log area, the database stops.
For these reasons, it is necessary to back up the log entries at regular intervals.
See also:
Backup Strategy [Page
39]
Saving Log Backups [Page
43]
Automatic Log Backup
Automatic log backup [Page 142] is recommended to ensure the security of data in production
systems.
If automatic log backup is activated, a log segment is saved as soon as it has been filled. This
log segment is then released again. The advantage of this is that a log area [Page
142]
overflow is almost impossible.
This mechanism is particularly recommended for all database instances [Page
132] in which
extensive write and change-intensive transactions are carried out. In this way, constant
monitoring of the usage level of the log area is not necessary.
As long as automatic log backup is active, you cannot start an interactive log
backup [Page 139]. However, you can carry out a data backup [Page 131].
You can only carry out automatic log backups in operating mode [Page 145]
ONLINE.
In the case of an automatic log backup, you can only copy the log entries to
version files [Page 153].
See also:
Backup Strategy [Page
39]
Saving Log Backups [Page
43]
Interactive Log Backup
You can use the interactive log backup [Page 142] to back up all the pages of the log area
[Page 142] that have been written since the last log backup.
If you back up the log entries in version files [Page 153], a version file is also generated for
the last log segment, which may not be full.
Prerequisites
A full data backup [Page 131] of the current database instance has been created.
User Manual: SAP DB 42