I cannot prove it, but I think it is so that when a job starts, that the
relative generation number always maps to the same absolute generation
number.
No, it is more basic than that, and goes back to the design of OS/360
40+ years ago.
Datasets are ENQed at JOB initiation, so a dataset used by a job is
ENQed from the start of the job until the end of the last step that uses
it (even if it doesn't get referenced for many steps). GDG absolute
generations are resolved at STEP initiation, using the catalog info
current at the time the step starts.
So, at job init, the absolute generation names are not known, so it ENQs
on the base GDG name. either SHR or EXCL depending on the JCL.
Another reason, updates to the GDG base must be serialized- you can't
have multiple jobs updating it. since a +n reference should specify
DISP NEW, this will ENQ on the GDG exclusive.
--
Bruce A. Black
Senior Software Developer for FDR
Innovation Data Processing 973-890-7300
personal: [EMAIL PROTECTED]
sales info: [EMAIL PROTECTED]
tech support: [EMAIL PROTECTED]
web: www.innovationdp.fdr.com
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