Sharing a CSD by CICS regions within a single MVS image (non-RLS)

The CICS® system definition data set (CSD) may be shared by a number of CICS regions within the same MVS™ image.

You can maintain the integrity of the CSD in this situation by coding SHAREOPTIONS(2) on the VSAM definition, as shown in the Figure 1. The CICS attributes of the CSD, as viewed by a given region, are defined in the system initialization parameters for that region.

You should consider defining:

One CICS region with read/write access (CSDACC=READWRITE) to the CSD. That region can use all the functions of CEDA, CEDB, and CEDC.
Other CICS regions with only read access (CSDACC=READONLY) to the CSD. Such CICS regions can use the CEDC transaction, and those functions of CEDA and CEDB that do not require write access to the CSD (for example, they can use INSTALL, EXPAND, and VIEW, but not DEFINE). You can enable such CICS regions to update the CSD, by using the procedure described in Sharing user access from several CICS regions.
Note: Read integrity is not guaranteed in a CICS region that has read-only access to a shared CSD. For example, if one CICS region that has full read/write access updates a shared CSD with new or changed definitions, another CICS region with read-only access might not obtain the updated information. This could happen if a control interval (CI) already held by a read-only region (before an update by a read/write region) is the same CI needed by the read-only region to obtain the updated definitions. In this situation, VSAM does not reread the data set, because it already holds the CI. However, you can minimize this VSAM restriction by specifying CSDLSRNO=NONE, and the minimum values for CSDBUFNI and CSDBUFND, but at the expense of degraded performance. See Specifying read integrity for the CSD for information about read integrity in a data set accessed in RLS mode.

If you define several CICS regions with read/write access to the CSD, those regions should all be at the latest level. Only one CICS region with read/write access can use a CEDA, CEDB, or CEDC transaction to access the CSD, because the VSAM SHAREOPTIONS(2) definition prevents other regions from opening the CSD.

If you are running CICS with the CSD defined as a recoverable resource (CSDRECOV=ALL), see Planning for backup and recovery for some special considerations.

You can use CEMT to change the file access attributes of the CSD, or you can use the EXEC CICS SET FILE command in an application program. However, ensure that the resulting attributes are at least equivalent to those defined either by CSDACC=READWRITE or CSDACC=READONLY. These parameters allow the following operations on the CSD:

READONLY: Read and browse.
READWRITE: Add, delete, update, read and browse.