Introduction to shared data tables

The CICS® shared data table facility is an extension of the CICS file management services.

The concept of shared data tables
Using shared data tables, all files that are defined as data tables can potentially be shared using cross-memory services. No changes are required to the file definitions for existing data tables.
Description of data tables
A CICS file is a representation of a data set on DASD. If you specify that the file is to use data table services, CICS copies the contents of the data set into an MVS™ data space when the file is opened and uses that copy whenever possible.
The data table sharing environment
The environment for sharing a data table is the same as for any file accessed in non-RLS mode.
The source data set for data tables
The source data set must be a base VSAM KSDS, not an alternate index. However, updates made to the KSDS via an alternate index are reflected in a CICS-maintained data table.
Data spaces for data tables
The data table records are stored in one or more MVS data spaces, whether the data table is to be shared by more than one region or not. A separate set of data spaces is used for each CICS region.
Global user exits for data tables
Three global user exits are provided to extend the normal processing done by data table services.
Shared data table services and remote file access
These diagrams illustrate the differences between using function shipping and using shared data table services to access a CICS file in another region.
How a data table is shared
Two operations, LOGON and CONNECT, establish a data table for sharing.

Parent topic: Access to databases and data sets