Database Recovery Services for DB2 LUW

Objective: Implement database recovery solutions with DB2 for Linux, UNIX, and Windows.

The DB2 for Linux, Unix, and Windows Recovery Services engagement is designed to provide your organization with customized assistance and skills transfer with advanced database recovery solutions with DB2 for Linux, Unix, and Windows.

This service engagement involves assistance with implementing customized scripts or procedures to automate and manage all aspects of DB2 for LUW recovery. This typically includes procedures to automate database backups, log archiving, database recovery, log retrieval, and roll-forward processing.

Background Information

Advanced Database Recovery refers to the implementation of customized scripts or procedures to automate and manage all aspects of DB2 recovery. These typically include backup, log archival, recovery, and roll -forward processing in what is typically termed a "Roll Forward Recovery with Off-line Log Archival" recovery environment. Off-line Log Archival provides for roll forward recovery in the event of a device or total system failure, as the database transaction logs are moved from the database transaction log path and onto another device or system.

DB2 provides three methods for database recovery. These are crash recovery, restore recovery, and roll forward recovery. Crash recovery is a method of recovery that attempts to resynchronize the database files with the database transaction log files in the event that the database is left in an otherwise inconsistent and unusable state. DB2 supports crash recovery right out of the box and by default it takes place automatically without manual intervention. Restore recovery is a method of recovery that attempts to restore an image of the database that was taken with the backup utility at a specific point in time. Finally roll forward recovery or point-in-time recovery is a method of recovery that attempts to reapply transactions to the database image after restore recovery has taken place. In order to support roll forward recovery you must change from circular logging to linear logging.

DB2 support two types of logging. Circular logging (as illustrated in the figure above) is the default setting. In this implementation logs are recycled as soon as they are no longer needed for crash recovery. Linear logging (as illustrated in the figure below) can easily be enabled by updating the database configuration parameter called LOGRETAIN. Note that after this parameter has been updated and the database deactivated you will need to take a complete off-line backup of the database before it can be accessed or you will have to disable this parameter to access the database without taking a backup.

Once linear logging has been enabled, you can choose to optionally archive log files off-line (see illustration below). Log archiving, the process of removing database transaction logs from the database server to a safer place, has been supported by DB2 for close to a decade now. The concept is relatively simple, when the database manager determinate that a log file is no longer needed it calls a user exit to archive the log. Once the log has been successfully archived by the user exit program, the database manager simply reuses the old log file by renaming it. The only minor detail that we left out is the user exit. Although IBM does provide some very good sample programs in \IBM\SQLLIB\SAMPLES\USEREXIT\, it should be noted that the u in user exit means you get to write it.

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