Overview of VSAM RLS

VSAM RLS processing involves support from multiple products:

CICS® Transaction Server
CICS VSAM Recovery (CICSVR)
DFSMS

VSAM RLS is a data set access mode that enables multiple address spaces, CICS application-owning regions on multiple systems, and batch jobs to access recoverable VSAM data sets at the same time.

With VSAM RLS, multiple CICS systems can directly access a shared VSAM data set, eliminating the need to ship functions between the application-owning regions and file-owning regions. CICS provides the logging, commit, and backout functions for VSAM recoverable data sets. VSAM RLS provides record-level serialization and cross-system caching. CICSVR provides a forward recovery utility.

The level of sharing that is allowed between applications is determined by whether or not a data set is recoverable. For example:

Both CICS and non-CICS jobs can have concurrent read or write access to nonrecoverable data sets. However, there is no coordination between CICS and non-CICS, so data integrity can be compromised.
Non-CICS jobs can have read-only access to recoverable data sets concurrently with CICS jobs, which can have read or write access.

VSAM RLS uses a coupling facility to perform data set-level locking, record locking, and data caching. VSAM RLS uses the conditional write and cross-invalidate functions of the coupling facility cache structure, thereby avoiding the need for control interval (CI) level locking. VSAM RLS uses the coupling facility caches as store-through caches. When a control interval of data is written, it is written to both the coupling facility cache and to direct access storage device (DASD). This ensures that problems occurring with a coupling facility cache do not result in the loss of VSAM data.