The CICS file-control component is a transactional file system built on top of VSAM. CICS file control provides transactional function such as commit, rollback, and forward recovery logging functions for recoverable data sets. Prior to VSAM RLS, CICS file control performs its own record-level locking. The VSAM data sets are accessed through a single CICS.

Users of multiple CICS regions have a file owning region (FOR) where the local file definitions reside. The access to the data set from the FOR is through the local file definition. Local data sets are accessed by the CICS application-owning region (AOR) submitting requests directly to VSAM. The remote definition contains information on the region and local filename. Sharing of data sets among regions or systems is achieved by having a remote file definition in any other region that wants to access the data set. If you are not using VSAM RLS, sharing is achieved by having remote definitions for the local file in any region that wants to share it. 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.

Related reading: For more information on using CICS to recover data sets, see Recovery and Restart Guide at http://publib.boulder.ibm.com/infocenter/cicsts/v3r1/index.jsp. For an overview of CICS, see that same CICS information center.