To recover a database to the point at which a backup was made, the backup file is the only input information that is required (for input to the database recovery utility). The following figure provides an overview of database recovery to a backup acquisition point.

Figure 21-1 Overview of database recovery to a backup acquisition point

Note

The following point must be kept in mind when a specific RDAREA is to be recovered to a backup acquisition point:

• When only the RDAREA in which the error occurred is recovered, it will lose synchronization with other RDAREAs.

For example, if an error occurs during execution of a definition SQL statement, and then only the user RDAREA in which the error occurred is recovered to a backup acquisition point, the data dictionary RDAREA will be at the most recent synchronization point before the error occurred. Therefore, the RDAREAs described in Table 6-3 RDAREAs to be backed up together must also be recovered from backups made at the same time.

(a) Transaction recovery

The point at which a transaction is completed is called a synchronization point. A synchronization point in which updates within a transaction become effective is called a commit, whereas if the updates become ineffective the synchronization point is called a rollback. Database recovery to the synchronization point of the most recently completed transaction at the time of an error is called recovery to the most recent synchronization point before an error occurred. A transaction that is being processed when an error occurs (a transaction that has not yet reached a synchronization point) is ineffective, which means that any update processing by the transaction cannot be recovered. The following figure shows recovery of a transaction.

Figure 21-2 Transaction recovery (recovery to the most recent synchronization point before an error occurred)

Explanation

Transactions A and B executed to completion and reached synchronization points; the database is recovered to these synchronization points.

Transactions C and D did not reach synchronization points, so their transaction processing is ineffective; these transactions cannot be recovered.

(b) Required input information

To recover a database to the most recent synchronization point before the error occurred, the following input information is required (for input to the database recovery utility):

• Backup file
• Unload log files^#

#: The unload log files that are required are those into which system log files subsequent to the backup acquisition point have been unloaded. If operation without unloading system log information is used, all system log files containing system log information subsequent to the backup acquisition point will be required.

The following figure provides an overview of database recovery to the most recent synchronization point before the error occurred.

Figure 21-3 Overview of database recovery to the most recent synchronization point before the error occurred

(c) Notes (important)

• The only RDAREA to be recovered is the one in which the error occurred.
• You must back up the RDAREA after it has been completely recovered. Otherwise, it will not be possible to recover the database from this synchronization point if an error occurs in this RDAREA subsequently.
• An unload log file to be used as input to the database recovery utility must be a regular file. Therefore, if the unload log files are saved on a medium such as a CMT or DAT, register them on the disk before executing the database recovery utility.
• In order to recover the master directory RDAREA using the system logs, HiRDB must be started with the pdstart -r command. If the system logs are used to recover an RDAREA other than the master directory RDAREA, HiRDB must be started with the pdstart command. Therefore, when recovering to the most recent synchronization point, the master directory RDAREA and other RDAREAs cannot be recovered simultaneously. For details about how to recover all RDAREAs to the most recent synchronization point, see 21.3.1 Example 1: Recovering all RDAREAs.

Database recovery to the synchronization point of a completed transaction at a time specified by the HiRDB administrator is called recovery to any synchronization point since a backup was made. It is not possible to recover the updates of a transaction that is being processed at the time specified by the HiRDB administrator (a transaction that has not yet reach a synchronization point). This is called recovery with a range specification. The following figure shows recovery with a range specification.

Figure 21-4 Recovery with a range specification

Explanation

Specify the recovery synchronization point in the -T option of the database recovery utility.

• To recover the database to synchronization point A, specify in the -T option a time after 9:10 but before 9:20 as the recovery end time.
• To recover the database to synchronization point B, specify in the -T option a time after 9:20 but before 9:30 as the recovery end time.
• To recover the database to synchronization point C (the synchronization point immediately before the error), the -T option need not be specified.

The input information (for input to the database recovery utility) that is required in order to recover the database to any synchronization point since a backup was made is the same as is needed for recovery to the most recent synchronization point before the error occurred.