In a recent note, Charles Mills said:
> Date: Fri, 27 May 2005 06:50:09 -0700
>
> How so? The JCL Reference says "NULLFILE has the same effect as coding
> the DD DUMMY parameter" and does not say that DUMMY precludes DCB=.
>
> -----Original Message-----
> From: IBM Mainframe Discussion List [mailto:[log in to unmask]] On
> Sent: Friday, May 27, 2005 6:02 AM
>
> The construction
>
> //<ddname> DD DUMMY
>
> is being misused here for a purpose for which it was never intended.
>
Please enlighten us. What, in your view, is the intended purpose
of "DUMMY"? (Citation welcomed.)
The OP said,
In orden to nullify the ISPF LOG ...
And in:
Title: z/OS V1R5.0 MVS JCL User's Guide
Document Number: SA22-7598-03
I read:
# 4.5.1 "z/OS V1R5.0 MVS JCL User's Guide"
__________________________________________________________
4.5.1 Processing Control by Suppressing Processing
To suppress processing of a data set, assign it a dummy status
by coding either of the following:
//ddname DD DUMMY,...
//ddname DD DSNAME=NULLFILE,...
Are you making some nice semantic distinction between "nullify"
and "suppress"?
To be fair, loc. cit. goes on to say:
The system ignores all parameters other than DUMMY or
DSNAME=NULLFILE and DCB. The DCB parameter must be coded if you
would code it for normal I/O operations. ...
Isn't the recommendation nowadays, for "normal I/O operations",
to allow SDB to calculate the BLKSIZE?
... For example, when an
OPEN routine requires a BLKSIZE specification to obtain buffers
and BLKSIZE is not specified in the DCB macro instruction, code
this information in the DD DCB parameter.
But I take this as an oversight, not corrected since pre-SDB
days. I understand the objective of SDB was to free the
programmer of the burden of calculating optimum block sizes,
a task for which the OS is now better suited than most
programmers (elite readers of this list excepted; I, for one,
am glad to let the OS do that chore for me). That benefit is
nullified to the extent that the programmer must ever perform
the calculation.
The implementation of SDB is deficient until it operates for
DUMMY as well as for real device types.
-- gil
--
StorageTek
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