CICS Regions

A CICS region is the home where CICS lives on the mainframe. Big shops run several regions and connect them, so work can be shared and the system keeps running even if one region has a problem.

What is a CICS region

• A region is a separate z/OS address space in which one CICS system runs.
• It is started as a started task with the DFHSIP program (you saw the startup JCL in an earlier topic).
• Each region has its own name, called the APPLID, for example CICSPROD or CICSTEST.
• One region can serve hundreds of terminals and run thousands of tasks.

Types of regions

• TOR - Terminal Owning Region - owns the terminals. Users sign on here.
• AOR - Application Owning Region - runs the application programs. Business logic executes here.
• FOR - File Owning Region - owns the files and data. File requests are shipped here.
• Splitting work this way balances the load: terminals, programs and files each get their own region.
• Small shops often run everything in a single region; large shops split into TORs, AORs and FORs.

Multi-Region Operation (MRO)

• MRO lets several CICS regions talk to each other and work as one system.
• Transaction routing - a transaction typed in the TOR runs its program in an AOR.
• Function shipping - a file request from one region is executed in the region that owns the file.
• Distributed Program Link (DPL) - a program in one region calls a program in another region.
• MRO gives scalability (add more AORs) and availability (one region can fail without stopping everything).

Controlling a region with CEMT

• CEMT is the CICS-supplied transaction used to look at and control a running region.
• Common CEMT commands every beginner should know:-
  CEMT INQUIRE TASK CEMT SET PROGRAM(CUSTMNT1) NEWCOPY CEMT SET FILE(CUSTMAS) OPEN CEMT PERFORM SHUTDOWN
• Note:- INQUIRE shows status, SET changes it, and PERFORM SHUTDOWN stops the region in an orderly way. Always confirm the APPLID before issuing SET or SHUTDOWN commands.