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. Figure 1. Diagram illustrating a Parallel Sysplex with RLS. This
view of RLS shows multiple CICS regions using VSAM RLS, through the
services of a SMSVSAM server in each MVS image.
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,
or
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.