DEFINE GENERATIONDATAGROUP

DEFININING GDG:

·        A generation data group is a group of related datasets, usually created in chronological order.

·        Before creating the first generation of a generation data group, two steps are required. 

1)     Creating a GDG base.

2)     A model must be created for the DCB parameters of the individual datasets to be created.

·        Syntax:

DEFINE GENERATIONDATAGROUP
    (NAME(entryname)
    LIMIT(limit)
    [EMPTY  |  NOEMPTY]
    [SCRATCH  |  NOSCRATCH]
    [TO(date)  |  FOR(days)])

    [CATALOG(catname[/password])] 

·        LIMIT specifies the maximum number (from 1 to 255) of generations that are to be kept.  

·        EMPTY specifies that all the generation datasets are to be uncataloged when the maximum is reached and another generation dataset is to be cataloged. 

·        NOEMPTY (the default) specifies that only the oldest generation dataset is to be uncataloged when the maximum is reached.

·        SCRATCH specifies that the generation dataset's entry is to be deleted from the Volume Table Of Contents when the generation dataset is uncataloged. The generation dataset ceases to exist. 

·        NOSCRATCH (the default) specifies that the generation dataset's entry is not to be removed from the VTOC when the generation dataset is uncataloged. 

MODEL DSCB:

·        When generation datasets are created, the DCB information for the new dataset must come from a model dataset. 

·        The model dataset does not occupy any storage space, but exists only as a VTOC entry. 

·        The model must be on the same volume where the catalog in which the generation data group is cataloged resides. 

·        Since the name for the GDG base is already in the catalog, the model (which also has the same name) cannot be cataloged. 

·        An alternative is to have a single model DSCB that is used for all generation datasets catalogued on a system pack, such as the System Residence.  

The following jobstream defines a Generation Data Group and also creates a model DSCB which can be used for the creation of the generation datasets.

//DEFGDG   JOB 'JAY MOSELEY',CLASS=A,MSGLEVEL=(1,1),MSGCLASS=A //IDCAMS  EXEC PGM=IDCAMS,REGION=4096K                        //MODEL    DD  DSN=MVS501.ACH.TRANS,DISP=(NEW,KEEP),      à not catalogued     //             UNIT=3350,VOL=SER=MVS501,SPACE=(TRK,0), à Space provided is 0       //             DCB=(RECFM=FB,LRECL=80,BLKSIZE=3120)           //SYSPRINT DD  SYSOUT=A                                       //SYSIN    DD  *                                                                                                              /* DELETE GENERATION DATA GROUP, IF IT EXISTS             */                                                                 DELETE MVS501.ACH.TRANS GENERATIONDATAGROUP                                                                                 /* DEFINE GENERATION DATA GROUP                           */                                                                 DEFINE GENERATIONDATAGROUP (                              -                NAME(MVS501.ACH.TRANS)                       -                LIMIT(5)                                     -                SCRATCH )                                                                                                       IF LASTCC = 0 THEN                                        -         LISTCAT ALL ENTRIES(MVS501.ACH.TRANS)

Note that the SPACE specified for the model is (TRK,0), so no space is reserved for the model.