MAXOPENTCBS

If you do not specify the MAXOPENTCBS parameter, the MXT value will be used to set a value for the MAXOPENTCBS parameter. For more information on how the value is set from MXT, see Open TCB management.

If you explicitly specify the MAXOPENTCBS parameter, or change its value dynamically using EXEC CICS SET DISPATCHER, then you must set it to a correct and optimum value. If you change MXT, however you choose to specify it (as a system initialization parameter, using CEMT, or EXEC CICS SET DISPATCHER, or using CICS Explorer®) you should review your explicit setting for MAXOPENTCBS. To revert to allowing CICS to set this parameter automatically after specifying it explicitly, you would have to reinitialize both the local and global catalogs. Before you reinitialize both the global and local catalogs, see The local catalog.

MAXOPENTCBS=number

Within this limit, there are no constraints on how many of the TCBs in the pool are L8 TCBs, and how many are L9 TCBs.

• L8 mode TCBs are used in the following circumstances:
  • For CICSKEY OPENAPI application programs.
  • For OPENAPI task-related user exits (TRUEs), for example the CICS-DB2 and WebSphere® MQ Attachment Facilities, and the CICS-DBCTL Database Adapter Transformer (DFHDBAT) when used with IMS Version 12 or later. TRUEs always run in CICSKEY.
  • By CICS itself, because CICS uses OPENAPI CICSKEY programs that run on L8 TCBs when accessing doc templates and HTTP static responses that are stored in z/OS® UNIX System Services files, or when processing web service requests and parsing XML. CICS also runs some security requests on L8 TCBs. CICS uses L8 TCBs when authenticating a password, password phrase or kerberos token when the original request was on the QR TCB.
• L9 mode TCBs are used for USERKEY OPENAPI application programs.

For more information about open TCBs, see Open TCB management.