Online Mode and Offline Mode (SAP Library - Database Administration (Oracle) with SAPDBA)

Online Mode and Offline Mode

Online Mode

Purpose

You can perform an online backup with the database running - that is, the users can continue to work normally. The management of database changes by the corresponding Oracle background processes is not affected either.

Tablespace online backups are inconsistent. The database can only be made consistent in a recovery if redo log entries from the period between BEGIN BACKUP and END BACKUP and exist and can be imported.

Prerequisites

An online backup is made using operating system utilities (for example, under the control of the SAP utility BRBACKUP). Because these utilities are not part of the database system, you must be informed about the starting point of a backup. In this way, a unique restart point is defined from which the recreation of all the files of a tablespace can be carried out in case of an error.

Procedure

The starting point of the backup is set using the command ALTER TABLESPACE <tablespace name> BEGIN BACKUP. The header of the tablespace files holds information on the checkpoint and redo log files. When the next redo log file switch or checkpoint occurs (normal database operations continue), the header information remains unchanged.

Based on this mechanism, all the files of a tablespace are copied with uniform header information specifying when the backup was started.

Once the backup of the tablespace is complete, the command ALTER TABLESPACE <tablespace name> END BACKUP ensures that the header information of the files is updated.

Offline Mode

Purpose

After an offline backup of the complete database, you have a backup of the database that is consistent. If you work with the database after the backup, the backup is consistent, but not up-to-date. In this case, you have to recover the database after you restore the backup.

Prerequisites

The database is closed during an offline backup; because the database cannot be accessed you cannot work with the R/3 System during an offline backup. However, the R/3 System does not have to be shut down for an offline backup. If the RECONNECT mechanism is set in the SAP start profiles, the connection to the R/3 System is remade after the database is restarted; this means that the information in the buffers of the R/3 System is not lost.