The Customer Information Control System (CICS®) file-control component is a transactional file system built on top of VSAM. Prior to VSAM RLS, CICS file control performs its own record-level locking. The VSAM data sets are accessed through a single CICS. Local data sets are accessed by the CICS application-owning region (AOR) submitting requests directly to VSAM. Remote (shared) data sets are accessed by the CICS AOR submitting (function shipping) a file-control request to a CICS file-owning region (FOR) and the FOR submitting a request to VSAM. CICS file control provides transactional function such as commit, rollback, and forward recovery logging functions for recoverable data sets. Figure 1 shows the AOR, FOR, and VSAM request flow prior to VSAM RLS.

Figure 1. CICS VSAM non-RLS access

The CICS AOR's function ships VSAM requests to access a specific data set to the CICS FOR that owns the file that is associated with that data set. This distributed access form of data sharing has existed in CICS for some time.

With VSAM RLS, multiple CICS AORs can directly share access to a VSAM data set without CICS function shipping. With VSAM RLS, CICS continues to provide the transactional functions. The transactional functions are not provided by VSAM RLS itself. VSAM RLS provides CF-based record-level locking and CF data caching. Figure 2 shows a CICS configuration with VSAM RLS.

Figure 2. CICS VSAM RLS

VSAM RLS is a multisystem server. The CICS AORs access the shared data sets by submitting requests directly to the VSAM RLS server. The server uses the CF to serialize access at the record level.