Defining, Generating, and Punching a DMCL › Adding Segments to the DMCL › Sharing Update Access to Data

Sharing Update Access to Data

What Is a Shared Area?

A shared area is an area that has been designated as shared. The sharability state of an area has meaning only for a central version that is a member of a data sharing group. An area that has been designated as shared can be updated concurrently by any member of the data sharing group that has access to the area in update. Only one group can have update access to an area at a time.

Designating an Area as Shared

You designate an area as shared by specifying the DATA SHARING YES clause when adding the segment to the DMCL or on a subsequent area override. The sharability state of an area can be changed at runtime by issuing a DCMT VARY SEGMENT or VARY AREA command, provided that the area's status is offline.

Shared Area Requirements

To share update access to an area, the following criteria must be met:

• All of the area's files must have an associated shared cache
• The area's characteristics must be identical in all members of the data sharing group that are to share access. These characteristics include:
  • Page range, page group, and number of records per page
  • Segment and area names
  • Page size
  • File mappings
  • IDMS file names
  • DSNAME and VOLSER of the associated disk files
• Within a data sharing group, no two shared areas can have overlapping page ranges within a page group
• Within a data sharing group, the combination of DSNAME and VOLSER must be unique for all IDMS files associated with shared areas
• A shared area cannot be native VSAM
• A shared area cannot be part of a dictionary controlled by CA Endevor/DB

If these conditions are not satisfied, you must alter your DMCL and segment definitions before declaring the area to be shared. Failure to do so will mean that one or more members of the group will be unable to access the area.

These conditions are waived on any CA IDMS system that is accessing the area in a transient retrieval mode regardless of whether the area has been designated as shared.