Preparing to use shared data tables support

To use shared data table support, you must perform the following tasks. Some of them will already have been done for an installation that currently uses function shipping or data tables.

About this task

  • Either ensure that the following modules are in an authorized system library in the LNKLST of the MVS™ system, or move them into a library in the LPALST concatenation.
    • DFHDTSVC and DFHDTCV, because all regions using shared data tables must use the same level of SVC code.
    • DFHMVRMS, the RESMGR exit stub, because CICS® JOBLIB/STEPLIB data sets are unavailable at end-of-memory.
    The following modules are placed by the installation of CICS into the target library SDFHLINK, which is normally included in the LNKLST concatenation.
    • If SDFHLINK is in the LNKLST concatenation, you should issue the operator command MODIFY LLA,REFRESH and wait for the confirmatory message CSV210I LIBRARY LOOKASIDE REFRESHED in order to make the modules available.
    • If SDFHLINK is not in the LNKLST concatenation, you should either copy the modules into a suitable library that is included and issue an LLA refresh, or copy the modules into a library in the LPALST concatenation and re-IPL the MVS system specifying CLPA.
  • If any files in any AOR are to use sharing, make sure that CICS is defined as an MVS subsystem.
  • Define security authorization so that FORs can act as shared data table servers and AORs can access files owned by servers, depending on the level of security required. In a single MVS image:
    • Any number of FORs can act as shared data table servers
    • A single AOR can use any number of these FORs
    • A single FOR can serve any number of AORs
    • A region can act as an AOR for one data table and as an FOR for a different data table.
  • If two FORs should have the same APPLID, at any given time only one of these FORs is used as a shared data table server. However, there is nothing to prevent one FOR acting as a shared data table server and another FOR, with the same APPLID, being used for function shipped requests. You should check that your operational procedures do not allow this because there is a risk that data table requests that use shared data table services are not directed to the same region as requests that use function shipping.
  • Define those files in the FOR that are data tables as either CICS-maintained data tables or user-maintained data tables.
  • Create additional remote file definitions in the AOR if required. No changes are needed to existing remote file definitions.
  • For any AOR that is to share data tables, specify ISC=YES as a system initialization parameter and define MRO or ISC links to the relevant FORs. For IP interconnectivity (IPIC) connections specify the equivalent system initialization parameter TCPIP=YES and define an IPIC link to the relevant FOR.
  • Before using shared data tables you might need to change some of your JCL statements, modify your operational procedures, or increase the value of the MAXUSER MVS initialization parameter. For more information, see MVS JCL requirements when using shared data tables.