At 07:06 -0700 on 11/17/2015, Lizette Koehler wrote about Re: Fastest
way to read OLDEST GDG entry:
I have heard the GDG limit in z/OS V2.2 will be higher, so it may
not be much of an issue for limit values.
Lizette
At the current time the limit is 255. Unless you are creating the
GDGs faster than you process them, you should be reading them fast
enough to keep the number under 255.
What you need to do is have your program find the oldest generation
(you can have it look for gdg(-254) and bump to -253/etc until you
get a FQDSN (DSN.Gxxxx.V00) or use some other method to get all the
generation names). So long as the limit is 255 and you have (lets
say) under 200 versions, a simple manual LISTC will tell you the
GXXXX of the earliest generation. Now submit your job passing the
XXXX and you are ready to go.
Now use SVC99 to allocate via the FQDSN not the relative GDG. When
processed delete it, bump the Gxxxx by 1 and process that file.
Eventually if you process faster than the create rate, you will get
to and process the then current GDG(0) and get a Does Not Exist when
you have bumped the Gxxxx to GDG(+1)'s name. You can then exit. The
only issue is when you get to G9999. GDG will handle this by creating
a new G0000 (or it may be G0001) but lising it as newer than G9999.
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