Understanding the DWWMSGA, DWWMSGB, DWWDMSG, and DWWDUMP data sets

Names of these message data sets should follow a specific naming convention described in the topic Understanding the DWWMSGA, DWWMSGB, DWWDMSG, and DWWDUMP data sets naming convention and look as follows:

• hlq.slq.DWWMSGA.systemname
• hlq.slq.DWWMSGB.systemname

When the CICS® VR server address space is activated, CICS® VR picks out one of the listed message data sets with more free space in it and allocates it as a current message data set to the DWWMSG ddname. It also issues the DWW302I message on a console to indicate the current message data set name. Various messages are written to this data set throughout various processing performed by the CICS® VR server address space.

The alternate message data set allocated to the DWWALT ddname is used when the CICS® VR server detects that the current message data set is becoming full. Then the CICS® VR server switches message data sets by performing the following actions:

• Close the DWWMSG data set, making it available for copy.
• Deallocate for both DWWMSG and DWWALT ddnames.
• Allocate the full message data set to the DWWALT ddname as an alternate.
• Allocate the other message data set to the DWWMSG ddname as a current.
• Open the current message data set DWWMSG file for writing to the data set from the beginning.

After switching message data sets, the CICS® VR server produces a message that informs which message data set is full. At this point, the first data set is available if you want to run a copy job to archive its contents. A copy job should use DISP=SHR for the copied message data set as shown in the this sample.

       //*------------------------------------------------------------
        //* Copy the full DWWMSG data set after switching
        //*------------------------------------------------------------
        //REPRO   EXEC PGM=IDCAMS
        //DWWMSGCP DD DSN=CICSVR.DWWMSGB.MVV1.COPY,
        //            DISP=(NEW,CATLG),UNIT=SYSDA,
        //            SPACE=(1330,200,,CONTIG),
        //            DCB=(RECFM=FBA,LRECL=133,BLKSIZE=1330,DSORG=PS)
        //INFILE   DD DSN=CICSVR.DWWMSGB.MVV1,DISP=SHR
        //SYSPRINT DD SYSOUT=*
        //SYSIN DD *
             REPRO INFILE(INFILE)                     -
                   OUTDATASET(CICSVR.DWWMSGB.MVV1.COPY)
       //*

The CICS® VR server will use the second data set until that becomes full, when it switches back to using the first data set and starts overwriting its contents.