Multiregion Operation (MRO)

Multiregion Operation lets several CICS regions on the same z/OS system work together as one system. Users see one CICS, but the work is spread across regions.

The diagram above shows the classic MRO layout: the terminal owning region takes user requests and routes the work to application, file, and data owning regions through XCF/IRC.

Why use MRO

• Split work by type: one region handles terminals, another runs applications, another owns files.
• If one region fails, the others keep running. Restart only the failed region.
• Add more application regions when load grows, without touching terminal definitions.
• Regions talk to each other through XCF (cross-system coupling facility) or IRC (interregion communication).

Region roles

• TOR - Terminal Owning Region: owns the terminals and routes transactions to the right region.
• AOR - Application Owning Region: runs the application programs. You can have many AORs.
• FOR - File Owning Region: owns the files. Application regions ship file requests to the FOR.
• DOR - Data Owning Region: owns data resources like DB2 or DL/I in some designs.

Defining an MRO connection

• Each pair of regions is connected with a CONNECTION definition using ACCESSMETHOD(XM).
• SESSIONS definitions set how many parallel conversations the regions can have.
• Use CEMT SET CONNECTION(name) ACQUIRED to start the connection, and INSERVICE to make it usable.
• CEDA DEFINE CONNECTION(AOR1) GROUP(MROCONN) ACCESSMETHOD(XM) SINGLESESS(NO) CEDA DEFINE SESSIONS(AOR1S) GROUP(MROCONN) CONNECTION(AOR1) MAXIMUM(50,10)
• The connection name must match the APPLID of the other region.