At 02:36 +0000 on 01/20/2009, Ted MacNEIL wrote about Re: GDG Question:
>That is because the GDG is in a VSAM catalog.
ICF catalogue -- different from VSAM.
True. I was using VSAM as the alternative to CVOL catalogs. ICF is
still VSAM but just a new way of handling the Catalog (as opposed to
Dataset) organization.
In the past when CVOL catalogs were used I think you were SOL since
there was no rollover
ability.
I don't recall it ever being a problem, even with CVOLs.
I started this business as a JCL jockey in Production Support, log
before UCC7 & UCC11 and their sucessors came out.
We used CVOLs for almost everything except IMS -- we didn't have
CICS, and DB2 wasn't available, yet.
We used GDG datasets all the time, and we never had a 'roll over' problem.
Since it requires that 10,000 Generations be created before there can
be a need to roll the Absolute Generation number over, it would take
a while and thus you might never have gotten to G9999. It is my
impression that with CVOL support, the organization of the GDG record
type had no provision for a Relative Generation Number that had an
lower Absolute Generation number than a prior Relative Generation
Number (ie: (0) = G0001 and (-1) = G9999). I seem to remember that
the recommendation was to reset when you got to G9500 or so. This was
not that hard a process since a simple rename (using Absolute
Generation Numbers) for DASD datasets would reset the numbers and
refresh the catalog. For Tape the process was a little more complex
since it involved the need to copy the tapes to new volumes under new
names. Since the Dataset Name in a Tape HDR1 label was only 17
Characters (not the full 44 Characters) and 9 of these were the
.GxxxxVxx suffix you could create the new tape using any prefix you
wanted. You then did the delete of the old GDG entries and creation
of the new ones (and deleted the temporary catalog entries if you had
cataloged the new tapes). Thus XXXX.GDGNAME.G9500V00 would be copied
as XXXX.TEMP.GDGNAME.G0001V00 (with only .GDGNAME.G0001V00 being in
the tape's HDR1 label), the XXXX.GDGNAME.G9500V00 entry (and the rest
of the 95XX ones) deleted, and a new XXXX.GDGNAME.G0001V00 catalog
entry created. Since all of the entries were first deleted, the new
entries would be created in the correct order. There might be a need
to delete and recreate the GDG Index CVOL entry since I have the
impression that it contained the next Generation number to use and
thus needed to be reset (since the current list of generations was
not consulted in processing a (+1) request.
Of course, my memory could be failing.
So might mine. It has been so long that I might
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