Generation Data group

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On an IBM mainframe computer a Generation Data Group (GDG) is a group of chronologically or functionally related datasets. GDGs are processed periodically, often by adding a new generation, retaining previous generations, and sometimes discarding the oldest generation.

A GDG base is created in the system catalog and keeps track of the generation numbers used for datasets in the group. The VSAM utility — IDCAMS — is used to define the GDG base.

  DEFINE GENERATIONDATAGROUP -           
  (NAME(GDG.BASE) -         
   LIMIT(10)  NOEMPTY SCRATCH -                        
   OWNER(USERID) -                      
  )

GDG has three parts:

  1. Index
  2. Model
  3. Generation

A sample program:

//SSS007TR JOB (20,FB3),'ANUJ',MSGLEVEL=(1,1),
//            CLASS=A,MSGCLASS=H,NOTIFY=&SYSUID                      
//STEP1    EXEC PGM=IDCAMS                                             
//SYSIN    DD   *                                                  
  DEFINE GDG (NAME(SSS007.TEST.GDG9) -                                
  LIMIT (5) -                                                        
  SCRATCH -                                                       
  NOEMPTY)                                                              
/*                                                                    
//SYSPRINT DD   SYSOUT=*                                               
//STEP2    EXEC PGM=IEFBR14                                             
//FILE1    DD   DSN=SSS007.TEST.GDG91,DISP=(,CATLG,DELETE),            
//             UNIT=SYSDA,SPACE=(CYL,(1,1),RLSE),                       
//             DCB=(RECFM=FB,LRECL=80,BLKSIZE=80)                      
//STEP3    EXEC PGM=IEFBR14                                             
//FILE1    DD   DSN=SSS007.TEST.GDG9(+1),DISP=(,CATLG,DELETE),         
//             UNIT=SYSDA,SPACE=(CYL,(1,1),RLSE),                      
//             DCB=SSS007.TEST.GDG91                                    
//                                                                     
//STEP4    EXEC PGM=IDCAMS                                              
//SYSIN    DD   *                                                       
  DELETE (SSS007.TEST.GDG9) GDG PURGE FORCE                            
/* 
//


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