CICS shared data tables

CICS file control commands can access shared data tables. Shared data tables offer a method of constructing, maintaining, and gaining rapid access to data records contained in tables held in virtual storage, above the 16 MB line. Each shared data table is associated with a VSAM KSDS, known as its source data set.

For more information about shared data tables, see Shared data tables overview.

A table is defined using the FILE resource. When a table is opened, CICS® builds it by extracting data from the table's corresponding source data set and loading it into virtual storage above the 16 MB line.

CICS supports two types of shared data table, as follows:

CICS-maintained tables (CMTs): This type of data table is kept in synchronization with its source data set by CICS. All changes to the data table are reflected in the source data set. Similarly all changes to the source data set are reflected in the data table.
The source for a CICS-maintained data table cannot be a file opened in RLS access mode.
User-maintained tables (UMTs): This type of data table is detached from its source data set after it has been loaded. Changes to the table are not automatically reflected in the source data set.

The full file control API appropriate to VSAM KSDS data sets is supported for CICS-maintained data tables. Requests that cannot be satisfied by reference to the data table result in calls to VSAM to access the source data set. Tables defined to be recoverable are supported with full integrity.

A subset of the file control API is supported for user-maintained tables. A table defined as recoverable participates in dynamic transaction backout but is not recovered at restart.