VSAM record-level sharing (RLS)
Record-level sharing (RLS) is an access mode for VSAM data sets supported by DFSMS 1.3 and later releases. RLS enables VSAM data to be shared, with full update capability, between many applications running in many CICS regions.
With RLS, CICS regions that share VSAM data sets can reside in one or more MVS images within an MVS parallel sysplex. This concept, in a parallel sysplex with VSAM RLS supporting a CICSplex, is illustrated in Figure 1.
Without RLS support (RLS=NO system initialization parameter), more than one CICS region cannot open the same VSAM data set concurrently using a non-RLS mode (such as LSR or NSR). These access modes mean that to share VSAM data between CICS regions, you must either:
- Use shared data tables,
- Allocate the VSAM data sets to one CICS region, a file-owning region (FOR), and function ship file requests from the applications to the FOR using either MRO, APPC, or IPIC connections.
With RLS support, multiple CICS regions can open the same data set concurrently. To use RLS:
- You need a level of DFSMS that supports RLS, and RLS=YES specified as a CICS system initialization parameter
- The CICS regions must all run in the same parallel sysplex
- There must be one SMSVSAM server started in each MVS image
- Specify RLSACCESS(YES) in the CICS file resource definition to provide full update capability for data sets accessed by multiple CICS regions.
You can specify RLS access for all files supported by CICS file control, except for the following:
- Key range data sets are not supported.
- VSAM clusters defined with the IMBED attribute are not supported. However, you can remove the IMBED attribute from the cluster definition without loss of function. Use the access method services REPRO function to move the data into a new cluster defined without the IMBED attribute. You can then use RLS access mode for files that reference the new cluster. (IMBED is a performance option that is generally unnecessary with modern caching disk controllers.)
- Opening individual components of a VSAM cluster (which is not supported by CICS for any mode of access).
- Temporary data sets are not supported.
- Key-sequence data sets (KSDS) in relative byte address (RBA) mode (OPTCDE=ADR) are not supported. Application programs that specify the RBA keyword on file control API commands for a KSDS opened RLS mode receive an INVREQ with RESP2 51 exception condition.
- Direct open of alternate index data is not supported in RLS access mode. However, path access to data is supported.
- VSAM catalogs and VVDS data sets are not supported.
Although you can specify RLS access for entry-sequenced data sets (ESDS), it is not recommended, because it can have a negative effect on the performance and availability of the data set when you are adding records. For more information, see VSAM and file control: improving performance.
For details of all the steps necessary to set up support for VSAM RLS, see Setting up VSAM RLS support.