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GDG

Generation Data Group

Enhanced Definition

A group of related sequential datasets organized chronologically, with each dataset called a generation. GDGs are useful for maintaining historical versions of files with automatic retention management.

Key Characteristics

- Chronological dataset organization
- Automatic generation numbering
- Retention limit enforcement
- Relative and absolute generation references
- Rolloff of oldest generations
GDG Structure:
- GDG Base: Catalog entry defining the group
- Generations: Individual datasets in the group
- Limit: Maximum number of generations to retain
Generation Naming:
- Relative: Reference to current (0) or previous (-1, -2, etc.)
- Absolute: Actual generation number (G0001V00)
- Creating New: Use (+1) to create next generation
GDG Base Attributes:
- LIMIT: Maximum generations (1-255 or 1-9999)
- EMPTY/NOEMPTY: Keep or delete generations when limit reached
- SCRATCH/NOSCRATCH: Delete or keep old generations on disk
- Extended: Support for more than 255 generations

//STEP1    EXEC PGM=MYPGM
//INPUT    DD DSN=PROD.DAILY.DATA(-1),DISP=SHR  (Yesterday's data)
//OUTPUT   DD DSN=PROD.DAILY.DATA(+1),          (Today's new gen)
//            DISP=(NEW,CATLG,DELETE),
//            UNIT=SYSDA,
//            SPACE=(CYL,(10,5))