User Guide

SAP AG November 2002
Instance Type
See Database instance type [Page 132]
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.
You can perform interactive log backups in operating mode [Page
145] ONLINE
or ADMIN.
You cannot perform any other backup while the interactive log backup is running.
See also:
Backup Strategy [Page
39]
Saving Log Backups [Page 43]
Isolation Level
The lock mode plays an important part in the lock behavior [Page 113]. The lock mode is
determined by specifying an isolation level.
By defining an isolation level, you specify whether and how shared locks [Page
114] and
exclusive locks [Page 115] are implicitly requested or released (Requesting and Releasing a
Lock [Page 115]).
The selected isolation level affects both the degree of concurrency and the guaranteed
consistency.
A high degree of concurrency is characterized by a state in which a maximum number of
concurrent transactions [Page
152] can process a database without long waiting periods
for locks to be released.
•
• As far as consistency is concerned, phenomena [Page
119] can arise through concurrent
access to the same database.
The lower the value of the isolation level, the higher the degree of concurrency and the lower
the guaranteed consistency. This means that a compromise between concurrency and
consistency that best suits the requirements of the application at hand must always be found.
You can use the CONNECT statement [See SAP DB Library]
to help define the isolation level
you require. The following isolation levels exist:
Isolation Level 0 [Page
117] (uncommitted)
•
Isolation Level 1 or 10 [Page
117] (committed)
•
Isolation Level 15 [Page
118]
•
Isolation Level 2 or 20 [Page
118] (repeatable)
•
User Manual: SAP DB 139