Without DFSMStvs, a CICS® system might have been available only during normal business hours. After business hours, the CICS system or application would be shut down for the supporting batch work to run. As soon as CICS stopped, backups were taken of key data sets as a point of recovery. Batch jobs could then be scheduled to run. If several jobs updated the same data set, they ran in sequence because they could not update the data set at the same time. After the updates were complete, a job would read the updated data and produce reports, and another backup would be taken. Finally, CICS could be restarted and become active again. However, the need to extend the availability of CICS has increased due to growing business volume.

DFSMStvs is an enhancement to VSAM RLS access that enables multiple batch update jobs and CICS to share access to the same data sets. DFSMStvs provides two-phase commit and backout protocols, as well as backout logging and forward recovery logging.

DFSMStvs provides transactional recovery directly within VSAM. DFSMStvs is an extension to VSAM RLS. It enables any job or application that is designed for data sharing to read-share or write-share VSAM recoverable data sets. VSAM RLS provides a server for sharing VSAM data sets in a sysplex. VSAM RLS uses coupling-facility-based locking and data caching to provide sysplex-scope locking and data access integrity, while DFSMStvs adds logging, commit, and backout processing.

DFSMStvs supports data sets that are defined as recoverable. That is, the log attribute for the data set is either UNDO (backout logging only) or ALL (backout and forward recovery logging). A batch job can open a recoverable data set for update in DFSMStvs mode. DFSMStvs provides the necessary transactional recovery for the data set. If a recoverable VSAM data set is opened for output and RLS is specified either in the JCL or the ACB, the data set is opened for DFSMStvs access.

Related reading: For information about programming language environments that support DFSMStvs, see z/OS DFSMStvs Administration Guide.