DCMT VARY Commands › DCMT VARY CHANGE TRACKING › DCMT VARY CHANGE TRACKING Usage

DCMT VARY CHANGE TRACKING Usage

Refreshing SYSTRK File Use

If the REFresh option is specified or change tracking is activated by specifying the ACTive option, the system replaces existing SYSTRK files with more recently formatted ones. This is useful in expanding the size of SYSTRK files because newer files can have more pages than existing files. To increase the amount of SYSTRK space available, all files must be replaced with files having the larger number of pages.

The following algorithm is used when refreshing SYSTRK file usage:

• A discovery process determines all SYSTRK files that are referenced either directly or indirectly through a model DD statement in the execution JCL.
• Each file is opened and read to determine its characteristics and control information.
  • Any file that cannot be opened, that encounters an I/O error or whose header is invalid, is discarded.
  • Any file whose characteristics are incompatible with the current SYSTRK file characteristics is discarded. To be compatible, its page size must be the same as the current page size and the number of pages must not be less than the current number of pages.
• All out-of-date files are brought up-to-date by copying the content from other files, or by writing new information.
• If the count of active mirrors is greater than the target, then the following actions occur:
  • The use of files is terminated until the count of active mirrors is equal to the target. The next file terminated is the one with the oldest initialization timestamp.
  • For each file whose use is terminated, the following actions occur:
    • If automatic file deletion is enabled, the file is deleted.

Note: This may take some time if the file is in use by another job.

• If automatic file deletion is disabled, a message is written indicating that the file is no longer being used and should be deleted manually.

• If the count of active mirrors is equal to the target, the current number of pages is set to be the smallest of all active files.

DCMT Commands that Require Active Change Tracking

If change tracking is in use for a CV, the following commands are impacted by the status of change tracking:

• DCMT VARY DMCL
• DCMT VARY FILE if it changes the data set name of the file
• DCMT VARY AREA or SEGMENT if it changes the permanent status of an area
• DCMT VARY JOURNAL FILE if it changes the data set name or the permanent status of a journal file

Note: If change tracking is inactive, these commands are prohibited. If it is disabled, a warning is issued if these commands are executed.