GDG's creation in JCL

Megha Gupta · New User Joined: 15 Mar 2012 Posts: 5 Location: India

If we have a GDG with limit as 10. and daily one generation use to create. Now, suppose 10 generations has created. on 11th day i have changed the limit of same GDG as 2. so, on 11th and 12th day 2 more generation will get create.

what would happen on 13th day? will job abend or it should override the 1st generation or it should override the 11th generation?

Thanks,
Megha

Nic Clouston · Posted: Tue Jan 21, 2014 7:10 pm

What happens depends on how your GDG base is defined. Why not set up a test gdg base and keep adding datasets to it and see what happens?

steve-myers · Posted: Tue Jan 21, 2014 7:13 pm

When you define a generation data group index, you specify three attributes -

LIMIT - the maximum number of data sets you can have in the generation data group at any one time.
EMPTY - Delete all the data sets in the group if you attempt to allocate a data set in excess of the limit. In 45+ years I have never seen a generation data group defined with this attribute.
SCRATCH - Delete the "oldest" data set in the group when you allocate a data set in excess of the limit.

You can use the IDCAMS ALTER command to change these attributes. However, if you attempt to reduce the LIMIT and there are more data sets in the group than in the new LIMIT, the command will be rejected, and the LIMIT will not be changed. Obviously you can delete the excess data sets before you change the limit.

You cannot do the scenario you have proposed.

See the DEFINE GENERATIONDATAGROUP topic in DFSMS AMS for Catalogs for the z/OS release you are running.

David Robinson · Active User Joined: 21 Dec 2011 Posts: 199 Location: UK

Phrzby Phil · Posted: Wed Jan 22, 2014 7:20 am

Nic's answer is THE BEST - you should always trust what a (very) simple test sequence tells you over what someone just says. Then you become the expert and teacher.

Megha Gupta · New User Joined: 15 Mar 2012 Posts: 5 Location: India

Thanks all for your suggestions!