The CICS® file-control program is a transactional file system built on top of VSAM. Without VSAM RLS, the CICS file-control program must perform 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) that submits requests directly to VSAM. Remote (shared) data sets are accessed by the CICS AOR that submits (function ships) a data set control request to a CICS file-owning region (FOR) and by the FOR that submits a request to VSAM.

Figure 1 illustrates the AOR, FOR, and VSAM request flow. CICS AORs function ship VSAM requests to access a specific data set to the CICS FOR that owns that data set. This distributed access form of data sharing has existed in CICS for some time.

Figure 1. CICS VSAM non-RLS access

Figure 2 illustrates how VSAM RLS enables multiple CICS transaction server AORs to access VSAM data sets for update while preserving data integrity. The updating regions can reside in any MVS™ image within a Parallel Sysplex®. Each MVS image has one SMSVSAM server. Each AOR that needs to access the VSAM data in RLS mode connects automatically to the SMSVSAM server address space. VSAM RLS stores locking information in a coupling-facility structure that SMSVSAM owns.

Figure 2. CICS VSAM RLS access

The CICS file-control program provides commit, backout, and forward recovery logging functions for VSAM recoverable data sets. With VSAM RLS, CICS continues to provide the transactional functions. VSAM RLS itself does not provide the transactional functions but does provide record locking based on a coupling facility as well as coupling-facility data caching.