CICS Multi-Region Operation (MRO)

What is Multi-Region Operation (MRO)?

Multi-Region Operation (MRO) is a CICS architecture that allows multiple CICS regions to operate as a coordinated system. Instead of running as isolated instances, MRO regions can communicate with each other, share resources, and distribute workload across multiple address spaces.

MRO was introduced in CICS/ESA and has evolved through subsequent versions to become a cornerstone of enterprise CICS deployments. It provides the foundation for building scalable, fault-tolerant applications that can handle increasing transaction volumes and provide continuous availability.

MRO Architecture Components

Region Types

MRO systems consist of different types of regions, each with specific responsibilities and characteristics:

Terminal Owning Regions (TORs)

Terminal Owning Regions are responsible for managing user terminals and handling user interactions. They receive user input, validate it, and route transactions to appropriate application regions. TORs typically handle:

• Terminal device management
• User authentication and authorization
• Input validation and formatting
• Transaction routing
• Screen presentation and formatting

Application Owning Regions (AORs)

Application Owning Regions contain the business logic and application programs. They process transactions, interact with databases, and perform the core business functions. AORs typically handle:

• Business logic execution
• Database operations
• File processing
• Transaction coordination
• Error handling and recovery

File Owning Regions (FORs)

File Owning Regions manage access to specific data resources such as VSAM files, databases, or other storage systems. They provide centralized data access and ensure data integrity across the MRO system. FORs typically handle:

• File and database access
• Data locking and synchronization
• Data recovery and backup
• Performance optimization
• Data security and access control

Auxiliary Control Regions (ACRs)

Auxiliary Control Regions provide specialized services such as monitoring, logging, or system management functions. They support the main application regions without directly handling user transactions. ACRs typically handle:

• System monitoring and alerting
• Performance data collection
• Logging and audit functions
• Backup and recovery coordination
• System administration tasks

MRO Communication Protocols

MRO regions communicate using several protocols that enable efficient data exchange and coordination:

Cross-Region Communication (XRC)

Cross-Region Communication is the primary mechanism for MRO regions to exchange data and control information. XRC uses the CICS intercommunication facilities to enable:

• Program-to-program communication
• Data transfer between regions
• Transaction routing and dispatching
• Resource sharing and coordination
• Error handling and recovery coordination

Function Shipping

Function shipping allows one region to request another region to perform specific operations on its behalf. This is commonly used for:

• File operations in remote regions
• Database access across regions
• Resource allocation and management
• System administration functions
• Performance monitoring and tuning

Asynchronous Processing

MRO supports asynchronous processing where regions can continue processing while waiting for responses from other regions. This enables:

• Improved throughput and responsiveness
• Better resource utilization
• Reduced waiting time for users
• Enhanced scalability
• Better fault tolerance

Resource Sharing in MRO

MRO enables various types of resource sharing across regions, improving efficiency and reducing duplication:

Shared Data Resources

Multiple regions can share access to common data resources such as:

• VSAM files and databases
• DB2 tables and views
• IMS databases and transactions
• Shared memory and storage
• Common configuration data

Program Libraries

MRO regions can share program libraries, reducing storage requirements and ensuring consistency:

• Load modules and programs
• Copybooks and include files
• Subroutines and utilities
• Common business logic
• Standard procedures and functions

System Resources

MRO enables sharing of system-level resources across regions:

• CPU and memory allocation
• I/O channels and devices
• Network connections and protocols
• Security and authentication services
• Monitoring and management tools

MRO Configuration and Setup

Setting up an MRO system requires careful planning and configuration of various components:

System Initialization Table (SIT)

The System Initialization Table contains parameters that control MRO behavior and configuration:

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SIT Parameters for MRO:
                  
MRO=YES                    # Enable MRO support
MROCONN=YES               # Enable MRO connections
MROMAX=10                 # Maximum number of MRO connections
MROTIMEOUT=300           # MRO connection timeout (seconds)
MROBUFSIZE=32768         # MRO buffer size
MROPROTOCOL=TCPIP        # MRO communication protocol
MROSECURITY=YES          # Enable MRO security
MROAUTH=USERID           # MRO authentication method

Resource Definition Online (RDO)

RDO is used to define MRO connections and resource sharing configurations:

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RDO Commands for MRO Setup:
 
DEFINE CONNECTION(MROCONN1) -
       GROUP(MROGROUP) -
       NETNAME(MRO1) -
       PROTOCOL(TCPIP) -
       SECURITY(USERID) -
       TIMEOUT(300)
 
DEFINE GROUP(MROGROUP) -
       TYPE(MRO) -
       MAXCONN(10) -
       AUTOCONN(YES)
 
DEFINE RESOURCE(MROFILE1) -
       GROUP(MROGROUP) -
       TYPE(FILE) -
       SHARED(YES)

JCL for MRO Startup

MRO regions require specific JCL parameters for proper initialization:

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//CICSMRO  JOB (ACCT),'MRO CICS',CLASS=A,MSGCLASS=X
//* CICS Multi-Region Operation Startup
//STEP1    EXEC PGM=DFHSIP,REGION=0M
//STEPLIB  DD  DSN=CICS.SDFHLOAD,DISP=SHR
//DFHCSD   DD  DSN=CICS.DFHCSD,DISP=SHR
//DFHSTART DD  DSN=CICS.DFHSTART,DISP=SHR
//DFHPARM  DD  *
SYSIDNT=MRO1
MRO=YES
MROCONN=YES
MROMAX=10
MROTIMEOUT=300
MROBUFSIZE=32768
MROPROTOCOL=TCPIP
MROSECURITY=YES
MROAUTH=USERID
//DFHCXRF DD  DSN=CICS.DFHCXRF,DISP=SHR
//DFHLOG  DD  DSN=CICS.DFHLOG,DISP=SHR
//DFHSNAP DD  DSN=CICS.DFHSNAP,DISP=SHR
//DFHAUXT DD  DSN=CICS.DFHAUXT,DISP=SHR
//DFHTEMP DD  DSN=CICS.DFHTEMP,DISP=SHR

MRO Programming Considerations

Developing applications for MRO environments requires understanding specific programming considerations and best practices:

Transaction Routing

Applications must be designed to handle transaction routing between regions:

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       IDENTIFICATION DIVISION.
       PROGRAM-ID. MRO-ROUTER.
       
       ENVIRONMENT DIVISION.
       DATA DIVISION.
       
       WORKING-STORAGE SECTION.
       01  ROUTING-TABLE.
           05  ROUTE-ENTRY OCCURS 10 TIMES.
               10  TRANS-ID        PIC X(4).
               10  TARGET-REGION   PIC X(8).
               10  REGION-TYPE     PIC X(3).
       
       01  CURRENT-TRANSACTION    PIC X(4).
       01  TARGET-REGION          PIC X(8).
       01  ROUTING-FOUND          PIC X VALUE 'N'.
       
       PROCEDURE DIVISION.
       
       MAIN-LOGIC.
           EXEC CICS RECEIVE
               INTO(CURRENT-TRANSACTION)
               LENGTH(LENGTH OF CURRENT-TRANSACTION)
           END-EXEC
           
           PERFORM FIND-ROUTE
           
           IF ROUTING-FOUND = 'Y'
               EXEC CICS LINK
                   PROGRAM('MRO-SENDER')
                   COMMAREA(TARGET-REGION)
               END-EXEC
           ELSE
               EXEC CICS ABEND
                   ABCODE('ROUT')
               END-EXEC
           END-IF
           
           EXEC CICS RETURN END-EXEC
       
       FIND-ROUTE.
           PERFORM VARYING WS-INDEX FROM 1 BY 1
               UNTIL WS-INDEX > 10 OR ROUTING-FOUND = 'Y'
               IF TRANS-ID(WS-INDEX) = CURRENT-TRANSACTION
                   MOVE TARGET-REGION(WS-INDEX) TO TARGET-REGION
                   MOVE 'Y' TO ROUTING-FOUND
               END-IF
           END-PERFORM.

Error Handling and Recovery

MRO applications must handle errors that can occur across region boundaries:

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       IDENTIFICATION DIVISION.
       PROGRAM-ID. MRO-ERROR-HANDLER.
       
       ENVIRONMENT DIVISION.
       DATA DIVISION.
       
       WORKING-STORAGE SECTION.
       01  ERROR-INFO.
           05  ERROR-CODE         PIC S9(8) COMP.
           05  ERROR-REGION       PIC X(8).
           05  ERROR-TRANSACTION  PIC X(4).
           05  ERROR-TIME         PIC X(8).
       
       01  RECOVERY-ACTION        PIC X(20).
       
       PROCEDURE DIVISION.
       
       MAIN-LOGIC.
           EXEC CICS HANDLE CONDITION
               ERROR(ERROR-ROUTINE)
               INVREQ(INVALID-REQUEST)
           END-EXEC
           
           EXEC CICS LINK
               PROGRAM('REMOTE-PROGRAM')
               COMMAREA(COMMUNICATION-AREA)
           END-EXEC
           
           EXEC CICS RETURN END-EXEC
       
       ERROR-ROUTINE.
           MOVE DFHEIBLK TO ERROR-INFO
           PERFORM LOG-ERROR
           PERFORM DETERMINE-RECOVERY
           PERFORM EXECUTE-RECOVERY
           EXEC CICS RETURN END-EXEC
       
       LOG-ERROR.
           EXEC CICS WRITEQ TD
               QUEUE('ERROR-LOG')
               FROM(ERROR-INFO)
           END-EXEC
       
       DETERMINE-RECOVERY.
           EVALUATE ERROR-CODE
               WHEN 1001
                   MOVE 'RETRY-OPERATION' TO RECOVERY-ACTION
               WHEN 1002
                   MOVE 'FALLBACK-REGION' TO RECOVERY-ACTION
               WHEN 1003
                   MOVE 'ROLLBACK-TRANSACTION' TO RECOVERY-ACTION
               WHEN OTHER
                   MOVE 'ABEND-TRANSACTION' TO RECOVERY-ACTION
           END-EVALUATE.

MRO Performance and Tuning

Optimizing MRO performance requires understanding various tuning parameters and monitoring techniques:

Buffer Management

Proper buffer sizing is crucial for MRO performance:

• MROBUFSIZE parameter controls communication buffer size
• Larger buffers improve throughput for large data transfers
• Smaller buffers reduce memory usage and improve response time
• Buffer size should match typical transaction data volumes
• Monitor buffer utilization and adjust as needed

Connection Pooling

MRO connection pooling improves performance by reusing connections:

• MROMAX parameter controls maximum connections
• Connection pooling reduces connection establishment overhead
• Monitor connection utilization and adjust pool size
• Balance between resource usage and performance
• Consider workload patterns when sizing connection pools

Timeout Configuration

Proper timeout configuration prevents resource hanging:

• MROTIMEOUT parameter controls connection timeout
• Too short timeouts can cause premature failures
• Too long timeouts can waste resources
• Monitor timeout patterns and adjust accordingly
• Consider network latency and application response times

MRO Security Considerations

Security is a critical aspect of MRO systems, requiring careful configuration and monitoring:

Authentication and Authorization

MRO security begins with proper authentication and authorization:

• MROSECURITY parameter enables security features
• MROAUTH parameter controls authentication method
• User ID validation across regions
• Resource access control and authorization
• Audit logging of cross-region operations

Network Security

Network security protects MRO communication channels:

• TCP/IP security and encryption
• Network isolation and segmentation
• Firewall configuration and access control
• Secure communication protocols
• Network monitoring and intrusion detection

Data Protection

Protecting data in transit and at rest is essential:

• Data encryption for sensitive information
• Secure data transmission protocols
• Access logging and monitoring
• Data backup and recovery procedures
• Compliance with security standards and regulations

MRO Monitoring and Troubleshooting

Effective monitoring and troubleshooting are essential for maintaining MRO system health:

Performance Monitoring

Monitor key MRO performance metrics:

• Cross-region communication response times
• Connection utilization and availability
• Buffer usage and efficiency
• Transaction routing performance
• Resource sharing effectiveness

Common Issues and Solutions

Be prepared to address common MRO issues:

• Connection failures and timeouts
• Performance degradation and bottlenecks
• Resource contention and deadlocks
• Security violations and access failures
• Data consistency and synchronization issues

Diagnostic Tools

Use available diagnostic tools for troubleshooting:

• CICS transaction monitoring (CEMT)
• Performance monitoring tools (RMF, SMF)
• Network diagnostic utilities
• Log analysis and correlation
• System trace and dump analysis

Knowledge Check: CICS Multi-Region Operation