Backup and Recovery › Backup Procedures › Backup While the DC/UCF System is Active

Backup While the DC/UCF System is Active

Types of Backup While System is Active

There are two types of backup that can be done while DC/UCF remains active:

• A quiesced backup during which no updates are made to the areas being copied
• A hot backup during which the areas that are copied are updated by transactions executing within the central version

While it is preferable to back up a database when it is quiesced, a site with high-availability requirements may not be able to disable updates long enough to complete the backup.

Considerations

If you decide to use a hot backup strategy, consider the following:

• The time to recover using a hot backup may be longer than with a backup produced while the area was quiesced due to additional steps in the recovery process.
• To recover using a file produced during a hot backup, all archive journal files created while the backup was taking place must also be available; without these files, the backup file cannot be used. Although the EXTRACT JOURNAL utility statement can be used to preprocess the journal images generated during this time period, the original archive files must also be available to perform a successful recovery.
• To ensure the availability of the archive journal files you should treat them in the same way as the backup file; for example, if a copy of the backup file is sent offsite, a copy of all corresponding archive files should also be sent offsite.

Note: For more information about the impact of a hot backup on recovering a database, see 21.5, “Manual Recovery".

Quiesced Backup Procedure

The procedure outlined below describes how to perform a quiesced backup.

Hot Backup Procedure

The procedure for a hot backup is similar to that for a quiesced backup, except that updates are re-enabled before the backup is complete. The procedure described next includes establishing a second quiesce point. This is not necessary if the appropriate recovery procedure is followed.

Note: For more information about the impact of a hot backup and a second quiesce point on recovery, see 21.5, "Manual Recovery".

Quiescing Update Activity

Both DCMT VARY AREA (and SEGMENT) and DCMT QUIESCE can be used to quiesce update activity in one or more areas of the database. Consider the following when choosing which of these to use:

• If DCMT VARY is used, tasks which subsequently attempt to access a target area in an update mode (or any mode if the area is varied offline) will receive an 0966 error status. Unless the application program handles this condition, the associated task will fail. If DCMT QUIESCE is used, such tasks will wait until update activity is restarted, unless their quiesce wait time is exceeded.
• DCMT QUIESCE provides more control over the quiesce operation. For example, it is possible to specify how long the quiesce operation should wait for conflicting tasks to finish and what action should be taken in the event that the quiesce point has not been reached in the specified time interval.
• In a data sharing environment, DCMT QUIESCE will quiesce update activity across all members of the data sharing group. DCMT VARY will quiesce update activity only within the DC/UCF system in which it is executed.
• DCMT QUIESCE can be used to automate much of the backup process.

More Information

• For more information about backup automation, see 21.2.4, "Automating the Backup Process".
• For more information about the DCMT system task, see the CA IDMS System Tasks and Operator Commands Guide.

Quiescing Update Activity for System Areas

When backing up a system area, such as a load area, it may be necessary to terminate predefined system run units by issuing a DCMT VARY RUN UNIT ... OFFLINE command. This will be necessary if predefined run units for the target area have been defined in the system definition and such run units access the area in update mode. You can determine this by issuing a DCMT DISPLAY RUN UNIT command.

Varying a system run unit offline does not prevent overflow run units from being started to service requests for the area. It simply terminates predefined run units of the specified type. Since varying an area offline will impact the system's ability to service requests for the area, it is advisable to quiesce update activity to system areas either by varying their status to retrieval or by using the DCMT QUIESCE command.

Depending on the options specified when issuing a DCMT VARY AREA, DCMT VARY SEGMENT, or DCMT QUIESCE command, the system may automatically terminate conflicting predefined system run units.

Note: For more information about when predefined system run units are automatically terminated, see the individual commands in the CA IDMS System Tasks and Operator Commands Guide.

Data Sharing Considerations

In a data sharing environment, whenever update activity is quiesced, it must be quiesced in all DC/UCF systems that are members of the data sharing group. If a DCMT QUIESCE command is used, then update activity will automatically be quiesced on all members within the group. If a DCMT VARY AREA or DCMT VARY SEGMENT command is used, it must be executed on each system that is a member of the group. This can be accomplished by broadcasting the DCMT command.

Note: For more information about broadcasting DCMT commands, see the CA IDMS System Tasks and Operator Commands Guide.