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Started task using a generation dataset


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M Lee Klein

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Joined: 08 Feb 2022
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PostPosted: Thu Apr 13, 2023 5:28 pm
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I have a started task uses a generation dataset for DDPRINT. This started task is only brought down for 5 minutes and then restarted. I need to modify the dataset after it's created but when the task starts up it creates a new generation of the dataset but the other generations are not accessible and are held by the started task.

Is there a way to release those datasets or must I make changes only while the started task is down?

MLK
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Joerg.Findeisen

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Joined: 15 Aug 2015
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PostPosted: Thu Apr 13, 2023 6:52 pm
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The STC will access the DSN by it's relative number I guess. Means, it's blocked for you to update. To be consistent with z/OS you can only update when the STC is down. Other options are possible, but shall not be discussed.
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Willy Jensen

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PostPosted: Thu Apr 13, 2023 8:37 pm
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That doesnt sound right. Can we see the JCL, please?
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enrico-sorichetti

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PostPosted: Thu Apr 13, 2023 10:16 pm
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quoting the manual
www.ibm.com/docs/en/zos/2.1.0?topic=jobs-submitting-multiple-update-generation-data-group
not the latest one but the concept has been the same since GDGs were born

Quote:

This topic provides guidelines that you can use when you submit multiple jobs that update a particular GDG:

No two jobs running concurrently can refer to the same GDG.

For batch or dynamic allocation jobs that specify relative generation numbers, the system enqueues the GDG base name as shared or exclusive, depending on the highest disposition that is used in the job. The GDG base name is exclusive if the highest job disposition is NEW or MOD. The GDG base name is shared if the highest job disposition is SHR. This safeguard prevents concurrent users from updating the GDG by adding or deleting generation data sets while other users are using the GDG.

For batch or dynamic allocation jobs that use absolute generation data set names, the system does not enqueue the GDG base. Multiple users are able to update the GDG by deleting or adding generation data sets at the same time. This situation does not affect the integrity of the GDG or generation data sets. However, jobs that use relative generation numbers might obtain the wrong generation, because the numbers can change. Even if you use absolute generation numbers, a job might accidentally replace a generation data set that another job is using.

The only time that you can use absolute generation numbers is when you need to run concurrent jobs that use the same GDG and at least one of the jobs uses a disposition of NEW or MOD. Ensure that the jobs do not accidentally overlay a generation data set that another job is using.
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vasanthz

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Joined: 28 Aug 2007
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PostPosted: Thu Apr 13, 2023 10:23 pm
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Quote:
The STC will access the DSN by it's relative number I guess.
I suspect the same.
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M Lee Klein

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PostPosted: Thu Apr 13, 2023 10:31 pm
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The jcl in the started task is

//DDPRINT DD DSN=BD.ADABAS.MPMPRNT(+1),
// DISP=(NEW,CATLG,DELETE),UNIT=SYSDA,
// SPACE=(TRK,(5,5),RLSE)

I was wanting to run a job that references BD.ADABAS.MPMPRNT.G2093v00.

So because I used a +1 in the started task jcl, I cannot access the generation?
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vasanthz

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PostPosted: Thu Apr 13, 2023 11:48 pm
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Quote:
So because I used a +1 in the started task jcl, I cannot access the generation?


Yes, since you use +1, you cannot access any generations in the GDG.
If your started task writes to the fully qualified generation with GXXXvYY at the end then the other generations would be accessible.
Although it could be a pain to make started task to use a absolute full name instead of the relative name
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Joerg.Findeisen

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PostPosted: Fri Apr 14, 2023 12:07 am
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To verify the current allocation, use ISRDDN or D GRS command. The GDG base and latest Generation is highly likely in-use, means not available for other updates until the STC has freed the resources.
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