Most Changes Can Be Implemented Dynamically
Most physical database changes can be made effective to a CV without recycling by issuing a DCMT VARY DMCL command.
Some changes require files to be deallocated and reallocated. The ability to deallocate and reallocate files dynamically depends on the operating system and the information provided in the file definition.
Note: For more information, see 7.14, "FILE Statements".
Some changes require that the use of areas or journal files be quiesced. CA IDMS does this automatically as part of the vary operation. However, this may take a significant amount of time if long-running transactions are in progress.
Note: For more information about the impact of each type of change, see 27.3, “Dynamic DMCL Management".
JCL Considerations
If CV's execution JCL contains DD statements for files whose data set name is changed by a DCMT VARY DMCL command, remove those DD statements before cycling the system.
Restart Considerations
If using VARY DMCL to implement your changes, you must consider how to handle an unanticipated failure during and after the operation.
The recommended approach is to use change tracking so that no manual intervention is needed to restart the CV after an abnormal termination. CA IDMS automatically restarts the system correctly using the information stored in the SYSTRK files.
If change tracking is not in effect, you are responsible for maintaining a copy of the old DMCL load module. You may need to restart the CV using the old DMCL if an abnormal termination occurs while the VARY DMCL command is in progress. Additionally, you may need to update the execution JCL before restarting the system to ensure that the correct data set names are being referenced.
Note: For more information on change tracking, see "Change Tracking" in the CA IDMS System Operations Guide.
Making Disk Journal File Changes
If making changes to disk journal files, do not change or replace all files at the same time. For example, you cannot change the dataset name or number of pages of all journal files with a single DCMT VARY DMCL command. To accomplish this, implement the changes in two separate operations, changing only some of the journal files each time.
Because of this restriction, you cannot change the page size of the disk journal files dynamically since all journal files must have the same page size. To change the journal page size, you must shutdown and restart the CV using a DMCL with the new journal buffer page size.
Data Sharing Considerations
In a data sharing environment, most changes to an area or its associated files will not take effect until the area is varied offline in all group members in which it is shared since most area (and associated file) characteristics must be identical across all sharing members. For a list of these characteristics, see Sharing Update Access to Data.
The following procedure is recommended for making shared area or file changes:
Note: For more information about data sharing, see the CA IDMS System Operations Guide.
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