What is GDG?

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What is GDG?

GDG - group of dataset that are logically or chronologically related, referred by name and a relative generation number - an integer which identifies the generation of a dataset and is coded in parenthese after dataset name. Absolute GDG name - GxxxxVyy, where xxxx-absolute generation number. yy-version number. Can be sequential, direct, partitioned. (VSAM - no). Must always be catsloged. Advantage - all dataset have the same name and system keeps track of adding new and retaining previous generations and deleting oldest successive generation. To create a GDG we create a GDG index in the system catelog with IDCAMS utility and then a model (prototype, DSCB) on the same volume to supply DCB information. Empty - when limit is reached all members are removed from the index, otherwise-only oldest. Scratch-removed members are uncataloged and deleted, otherwise - removed and uncataloged, but remain in the system (not members of GDG any more). GDG number is updated at the end of the job. If number is not specified all generations will be provessed from the beginning.

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Other Job Interview Questions

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• What does the statements: typrun=scan and typrun = hold do in a JCL statement?
• What does the keyword DCB mean and what are some of the keywords associated with it ?
• What is STEPLIB , JOBLIB ? What is it used for ?
• How do you submit JCL via a COBOL program?
• The maximum number of steps in a job?
• What is the purpose and meaning of the REGION keyword and what JCL statement is it associated with ?
• How is a new GDG coded?
• How do you restart a step in JCL?
• How is the keyword DUMMY used in JCL ?
• More...