What is a GDG?

What is a GDG?

GDG- It is the acronynm for Generation Data Group. GDG is a group of chronologically related datasets. The individual generation of datasets within a GDG is called generation data set (GDS). These GDS have sequential generations as the absolute names. These can also be referred by their relative names.

GDG(0)- Refers to the current generation of  GDG

GDG(-1)- Refers to the previous generation of  GDG

GDG(+1)- Refers to the next generation of  GDG

Example:- my.gdg.name.GnnnVnn

Where

         my.gdg.name is  Group name or the GDG base name

         Gnnnn    –           Absolute generation number ( 0000 to 9999 )

         Vnn        –           Version of that generation. (00 to 99)

How to define a GDG base?

A GDG base can be defined by IDCAMS utility.

Example:

            //DEFINE          EXEC           PGM=IDCAMS

            //SYSPRINT   DD      SYSOUT=A

            //SYSIN          DD *

                        DEFINE GDG (NAME(my.gdg.name) SCRATCH-

                        NOEMPTY-

                        LIMIT(30))

            /*

The various parameters used for defining the GDG are as below

Name:- Name of the GDG to be created.

Limit(n):-Maximum number of generations that can exist at a time.

Empty:-This option will delete all the older generations if the limit of generations is reached

For Eg:- If a GDG is defined with a limit of 30 and 31^st generation is created then all the old 30 generations are deleted and the 31^st generation is created.

NoEmpty:- This option will delete the oldest generation if the limit of generations is reached 

For Eg:- If a GDG is defined with a limit of 30 and 31^st generation is created then all the first generation will be deleted and the 31^st generation will be created. So at the end there will be generations from 2^nd to 31^st

Scratch:-This option will delete the generation completely if the dataset is deleted.  NoScratch-> This option will uncatalog the dataset if the dataset is deleted.