On 2019-08-07 5:08 AM, Carmen Vitullo wrote:
I suspect dynamic allocation may be doing more that the IEFBR14 possibly?
Well, DYNALLOC is certainly doing more that the job step initiation when
it comes to allocation.
Device allocation at step-start time is a largely CPU-bound affair with
the only I/O usually being for catalog look-ups. That is why something like
//MY DD DD DSN=FRED,DISP=OLD,UNIT=3390,VOL=SER=MYVOL1
will get a S213-04 at OPEN time when FRED does not exist.
DYNALLOC will check that FRED exists on the volume - yes! it does "lots"
of I/O to the data set's volume which batch device allocation does not
perform.
Data set name enqueue is done before device allocation, and most of it
is done at job start time for data sets mentioned in JCL. DYNALLOC has
to do the ENQ when it is called before looking at devices.
Cheers,
Greg
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