The XRF control data set

The XRF control data set is used:

CAVM rejects a request from a CICS job to sign on as the active CICS region if the XRF control data set shows that an active CICS region is already present, or that a takeover is in progress. This ensures that the integrity of files and databases cannot be lost as a result of uncontrolled concurrent updating by two or more active CICS regions. As soon as an active or alternate CICS regions signs on, it starts to write its own surveillance signals, and to look for its partner’s surveillance signals.

JCL to define the XRF control data set

You must define the XRF control data set, but not initialize it. You can use the JCL statements in Figure 18 to define the XRF control data set. Alternatively, you can run the CICS-supplied job DFHDEFDS to define the XRF control data set as one of the data sets for a CICS region. For information about the DFHDEFDS job, see the CICS Transaction Server for z/OS® Installation Guide">.

Figure 18. Sample job to define the XRF control data set
//CICSCTL   JOB   'accounting info',name,MSGCLASS=A
//XRCTL     EXEC  PGM=IDCAMS
//SYSPRINT  DD    SYSOUT=A
//SYSIN     DD    *
       DEFINE CLUSTER -
                (NAME(CICSTS31.CICS.applid.DFHXRCTL) -
                 RECORDSIZE(4089 4089)         -                   1 
                 CONTROLINTERVALSIZE(4096)     -                   2 
                 RECORDS(4)                    -
                 NIXD                          -
                 SHAREOPTIONS(3,3)             -                   3 
                 VOLUMES(volid1))              -
              DATA                             -                   4 
                (NAME(CICSTS31.CICS.applid.DFHXRCTL.DATA))
/*
//

Notes:

 1  The RECORDSIZE must be at least 4089.

 2  The control interval sizes of the XRF control data set and the XRF message data set must be equal, and at least 4096 bytes.

 3  The SHAREOPTIONS must be specified as 3,3.

 4  The data set must be VSAM-ESDS.

Serializing access to the XRF control data set

Access to the XRF control data set must be serialized during the critical sections of CAVM signon, sign-off, and takeover processing. The correct choice of volume is important because this serialization is provided by RESERVE/RELEASE (DEQ) logic. For example, it would be unwise to place an XRF control data set on the same volume as the JES checkpoint data set. If you use global resource serialization (GRS) you must not convert this RESERVE, which uses the qname SYSCICSX, to a global ENQ.

Space calculations

Only four control intervals are needed.

Job control statements for CICS execution

The DD name required for CICS execution is DFHXRCTL. The following is an example of the JCL statement required:

//DFHXRCTL  DD    DSN=CICSTS31.CICS.applid.DFHXRCTL,DISP=SHR
[[ Contents Previous Page | Next Page Index ]]