The two methods described below are available for moving the time back. Select the one that is most appropriate for your system.

Method 1:

This method starts HiRDB after waiting for the amount of time by which the time is moved back (for example, one hour if the time is moved back by one hour). Select this method in the following cases:

• It is possible to stop services while waiting for the amount of time by which the time is moved back.
• The amount of time by which the time is moved back is short.
• Real Time SAN Replication based on the log-only synchronization method is used.
• Backups are acquired and recovery is executed using the NetBackup linkage facility.

Method 2:

This method does not wait for the amount of time by which the time is moved back. However, you need to move back the time while taking steps to ensure that the date and time information held by HiRDB is not affected. Select this method when it is necessary to limit the time during which services are stopped.

When you use either of these methods to move back the time, you must take steps to ensure that HiRDB operation is not adversely affected. The following table shows the conditions that require action, the actions to take, and the effects of incorrect actions.

Table 9-5 Conditions that require action when the time is moved back, the actions to take, and the effects of incorrect actions

Conditions that require action	Method of moving the time back	Action to take	Effects of incorrect actions
The data extraction facility of HiRDB Datareplicator is being used.	Method 1 or 2	HiRDB Datareplicator references the time information in the system log. Therefore, you must take steps to ensure that moving back the time will not cause HiRDB Datareplicator to malfunction.	Problems such as destruction of the target database might occur.
Operation without unloading system log is used	Method 1 or 2	To acquire a log point, execute the database copy utility (pdcopy) with the -z option specified after the time is moved back.	If a log point has not been acquired, the database cannot be restored to the most recent state should an error occur.
Message log files are displayed using the pdcat command.	Method 2	Message log files record the messages that are output by HiRDB in order of time. The pdcat command imports the message log files and display them according to time. Therefore, you must take steps to ensure that moving back the time will not corrupt the time information, causing the display result by the pdcat command to become corrupted.	HiRDB will not be able to reference the messages that were issued before the time was moved back.
Statistical information has been acquired.	Method 2	When the time is moved back, the statistical information that is output to the statistics log file is no longer arranged according to time. Take steps to make sure that the statistical information accumulation result acquired by the statistics analysis utility (pdstedit) does not become corrupted.	It will not be possible to analyze the statistical information that was acquired before the time was moved back.
Time is moved back using method 2.	Method 2	Before moving back the time, you must unload the system log files, save the unloaded files, and then delete them.	It will not be possible to restore the database after an error.
		After moving back the time, you must acquire a backup to prepare for a HiRDB error, and initialize the system log file and the synchronization point dump file.	If an error occurs after the time has been moved back, the database cannot be restored to the state it was in after the time was moved back.