Coupling Facility

Customization › Multi-Access Spool (MAS) › Coupling Facility

Coupling Facility

If all the members in a MAS complex have access to the same Coupling Facility, we recommend that you use a Coupling Facility Structure for communication. All changes to the file queue are exchanged to the other MAS members through the Coupling Facility.

The MAS member with the lowest system number automatically becomes the CKPT owner, which is responsible for writing all changes to the checkpoint data set(s). The other MAS members are updated through the Coupling Facility, so they have no need to access the checkpoint data set, so RESERVE/RELEASE is avoided.

CA Spool supports System-Managed CF Structure Rebuild. If the Coupling Facility is switched to a backup Coupling Facility, the operating system copies the old structure data to the new structure, providing a planned reconfiguration capability.

CA Spool supports System-Managed CF Structure Duplexing, so a backup copy of the CA Spool CF structure is automatically maintained on a secondary coupling facility. In case of failure, the system can automatically switch to the duplex copy of the CF structure and continue running with no disruption or performance degradation.

To use a Coupling Facility Structure

Update your Coupling Facility Policy Data set to reflect the definition of the Coupling Facility structure and run the Administrative Data Utility as follows:

//CFRMUPDT JOB ...                             
//*                                            
//STEP1  EXEC PGM=IXCMIAPU                     
//SYSPRINT DD   SYSOUT=*                       
//SYSABEND DD   SYSOUT=*                       
//SYSIN    DD   *                              
                                               
     DATA TYPE(CFRM) REPORT(YES)               
                                               
     DEFINE POLICY NAME(**policy**) REPLACE(YES)
                                               
        CF NAME(**couplet1**)                  
               ...                             
     ...                                       
                                               
     STRUCTURE NAME(**ESF_STRUCT**) SIZE(8192) 
             PREFLIST(**couplet1**)            
     ...                                       
                                               
/*

Note: The required size of the structure for CA Spool within the Coupling Facility may change when the CFLEVEL changes. IBM's web site provides a CFSIZER utility that can be used to determine the correct size at the current CFLEVEL.

The following values can be used on the OEM page of that utility:

List Headers - 8
Lock Table Entry Count - 8
Maximum Number of Data Elements per Entry - 64
Adjunct Data - No
Reference Option - None
Maximum Number of List Entries - 1
Maximum Number of Data Elements - 64
Data Element Size Descriptor - ELEMCHAR
Data Element Size Value - 2

Specify the Coupling Facility structure name on the primary CHKPTDS statement as follows:
```
CHKPTDS NUM=1,DSNAME=SYS1.ESFCHKPT,STRNAME=**ESF_STRUCT**
```
Restart all members in the MAS/EMAS complex.