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Regarding Dummy Parameter

 
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saurabh39
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Joined: 11 Apr 2008
Posts: 144
Location: Jamshedpur

PostPosted: Mon Sep 12, 2011 11:09 pm    Post subject: Regarding Dummy Parameter
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Hi All,

While analyzing the production JCL, i came across following dataset concatenation code -

Code:

//SNDUPDFL DD  DSN=XXXX.YYYYY.SNDUPD03,DISP=OLD   
//         DD  DSN=XXXX.YYYYY.SNDUPD04,DISP=OLD   
//         DD  DSN=XXXX.YYYYY.SNDUPD05,DISP=OLD   
//*        DD  DSN=XXXX.YYYYY.SNDUPD06,DISP=OLD   
//*        DD  DSN=XXXX.YYYYY.SNDUPD07,DISP=OLD   
//         DD  DSN=XXXX.YYYYY.SNDUPD08,DISP=OLD   
//*        DD  DSN=XXXX.YYYYY.SNDUPD10,DISP=OLD   
//         DD  DUMMY                             
//*        DD  DSN=XXXX.YYYYY.SNDUPD14,DISP=OLD   
//*        DD  DSN=XXXX.YYYYY.SNDUPD16,DISP=OLD   
//         DD  DSN=XXXX.YYYYY.SNDUPD18,DISP=OLD   
//         DD  DSN=XXXX.YYYYY.SNDUPD19,DISP=OLD   
//         DD  DSN=XXXX.YYYYY.SNDUPD21,DISP=OLD   
//*       DD  DSN=XXXX.YYYYY.SNDUPD24,DISP=OLD   
//*       DD  DSN=XXXX.YYYYY.SNDUPD26,DISP=OLD   
//*       DD  DSN=XXXX.YYYYY.SNDUPD33,DISP=OLD 
//         DD  DUMMY                             
//*       DD  DSN=XXXX.YYYYY.SNDUPD34,DISP=OLD           
//*       DD  DSN=XXXX.YYYYY.SNDUPD35,DISP=OLD         
//         DD  DUMMY                                     
//         DD  DSN=XXXX.YYYYY.SNDUPD36,DISP=OLD           
//*       DD  DSN=XXXX.YYYYY.SNDUPD37,DISP=OLD         
//         DD  DUMMY                                     
//*       DD  DSN=XXXX.YYYYY.SNDUPD11,DISP=OLD         
//*
                                             


When processing these files, the COBOL Code is processing only the first 4 files(files above dummy statement).

In the IBM manual it states that -

Quote:
The system treats data sets concatenated to a DUMMY data set as dummy data sets in that I/O operations are bypassed. However, the system performs disposition processing and allocates devices and storage for any concatenated data sets.


It says I/O opeartions are bypassed. Now the question, when they say I/O operations are bypassed do they mean nothing will be read after dummy statement. I am having difficulty in understanding that part of statement. As per the program behaviour I/O operations have been performed till first dummy statement is found and after that nothing was read. So the I/O operations will be bypassed from DD Dummy statement onwards. Please correct me, if i am wrong.
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Nic Clouston

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Joined: 10 May 2007
Posts: 1787
Location: UK

PostPosted: Tue Sep 13, 2011 12:07 am    Post subject:
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Quote:
The system treats data sets concatenated to a DUMMY data set as dummy data sets in that I/O operations are bypassed


You obviously do not understand the text in bold in that you do not seem to realise that the text 'I/O....bypassed' relates to the dummy datasets and its concatenated datasets. Also, the fact that the program managed to only read the files before the first DUMMY should have answered your question.
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Robert Sample

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Joined: 06 Jun 2008
Posts: 8055
Location: East Dubuque, Illinois, USA

PostPosted: Tue Sep 13, 2011 12:15 am    Post subject:
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From section 4.5.1 of the JCL User's Guide manual:
Quote:
Requests to Read or Write a Dummy Data Set

When the program asks to read a dummy data set, an end-of-data-set exit is taken immediately. When the program writes to the dummy data set, the request is recognized but no data is transmitted. VSAM supports dummy data sets for both read and write processing. BSAM and QSAM support requests to write to a dummy data set. If any other access method is used, the job is terminated.
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dick scherrer

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Joined: 23 Nov 2006
Posts: 19270
Location: Inside the Matrix

PostPosted: Tue Sep 13, 2011 12:17 am    Post subject:
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Hello,

The JCL posted is at best confusing to look at.

Suggest it be cleaned up or documented as to why all of the nonsense is left in the convatenation . . .
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Anuj Dhawan

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Joined: 22 Apr 2006
Posts: 6258
Location: Mumbai, India

PostPosted: Mon Sep 19, 2011 8:32 pm    Post subject: Re: Regarding Dummy Parameter
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saurabh39 wrote:
It says I/O opeartions are bypassed. Now the question, when they say I/O operations are bypassed do they mean nothing will be read after dummy statement. I am having difficulty in understanding that part of statement. As per the program behaviour I/O operations have been performed till first dummy statement is found and after that nothing was read. So the I/O operations will be bypassed from DD Dummy statement onwards. Please correct me, if i am wrong.
They are bypassed once they get to DUMMY, before that it is not.
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