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prakal Beginner
Joined: 14 Mar 2003 Posts: 22 Topics: 1
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Posted: Fri Mar 14, 2003 11:16 am Post subject: Dummy Vs Empty Files |
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Could you please let me know, what are the differences/advantages of using DSN=DUMMY and DSN=FILEA, where FILEA is empty in both PSE and VSAM.
Thanks
prak |
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sanat Beginner
Joined: 15 Feb 2003 Posts: 11 Topics: 7 Location: chennai
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Posted: Fri Mar 14, 2003 12:20 pm Post subject: |
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Hi,
I have a supplementary question to the above one. Is there any difference between using DUMMY file (DD DUMMY) and NULLFILE (DD DSN=NULLFILE).
This was an interview question. I refd. some JCL books and but could not make out anything.
Sanat. |
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kolusu Site Admin
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Joined: 26 Nov 2002 Posts: 12369 Topics: 75 Location: San Jose
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Posted: Fri Mar 14, 2003 1:23 pm Post subject: |
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Prakal,
The advantages of coding a dummy versus DSN=FILEA where the file is empty are as follows.
when you code DD DUMMY it does the following
- No device or external storage space is to be allocated to the data set.
- No disposition processing is to be performed on the data set.
- I/O operations are bypassed
On the other case DSN=FILEA , even though the file is empty the system performs all the above mentioned tasks.
Sanat : your question has already discussed before .check this link
http://www.mvsforums.com/helpboards/viewtopic.php?t=374
Hope this helps...
cheers
kolusu |
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prakal Beginner
Joined: 14 Mar 2003 Posts: 22 Topics: 1
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Posted: Fri Mar 14, 2003 4:04 pm Post subject: |
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Thanks a lot for the explanation Kolusu.
Prakal. |
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slade Intermediate
Joined: 07 Feb 2003 Posts: 266 Topics: 1 Location: Edison, NJ USA
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Posted: Mon Mar 17, 2003 6:17 pm Post subject: |
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Hi Prakal,
A big difference between the two to remember is when using them in concatenations:
When a dummy file is used in a concat, processing goes to EOF even if there are other non-empty files following the dummy file.
When this condition exists with an empty file, the following files are processed by the pgm.
NOTE!!!: The "empty" file described here has been subject to close processing and contains an appropriate EOF indicator.
Regards, Jack. |
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prakal Beginner
Joined: 14 Mar 2003 Posts: 22 Topics: 1
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Posted: Wed Mar 19, 2003 1:38 pm Post subject: |
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Thanks for the information Jack. |
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