MVSFORUMS.com

prakal · Beginner Joined: 14 Mar 2003 Posts: 22 Topics: 1

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

sanat · Posted: Fri Mar 14, 2003 12:20 pm Post subject:

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.

kolusu · Posted: Fri Mar 14, 2003 1:23 pm Post subject:

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

prakal · Beginner Joined: 14 Mar 2003 Posts: 22 Topics: 1

Thanks a lot for the explanation Kolusu.

Prakal.

slade · Posted: Mon Mar 17, 2003 6:17 pm Post subject:

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.

prakal · Beginner Joined: 14 Mar 2003 Posts: 22 Topics: 1

Thanks for the information Jack.