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

The CICS® VR server allocates two message data sets at the server activation.

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: When the CICS VR server address space is activated, CICS VR picks out one of the above 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 will be written to this data set throughout various processing performed by the CICS VR server address space.

The other message data set is allocated to the DWWALT ddname as an alternate message data set. If both message data sets are full, CICS VR uses the hlq.slq.DWWMSGA.systemname data set as a current and empties it.

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: After switching message data sets, the CICS VR server produces a message informing which message data set is full. At this point the first dataset is available if a customer wishes 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 sample below.
       //*------------------------------------------------------------
        //* 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 dataset until that becomes full, when it switches back to using the first data set and starts overwriting its contents.

In addition, the CICS VR server address space allocates single data sets to both the DWWDMSG and DWWDUMP ddnames. Therefore, if a problem occurs within the CICS VR server address space, various tracing and dump information can be written to the data sets allocated to the DWWDMSG and DWWDUMP ddnames that could help during problem resolution.

When the CICS VR server detects that the diagnostic message data set or the dump data set is becoming full, it rewrites it without producing any message on a console.

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