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NULLFILE on ICEGENER Utility

 
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Ashishpanpaliya

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Joined: 13 Oct 2017
Posts: 8
Location: India

PostPosted: Wed Nov 08, 2017 10:45 pm    Post subject: NULLFILE on ICEGENER Utility
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I am doing the impact analysis to trace back the file. Since SYSIN DD is dummy, therefore its will do nothing on SYSUT1 and SYSUT2.
But I couldn't understand the purpose of Nullfile. I tried to investigate in manual/google but couldn't find anything. Apologies if I missed anything.


Code:
//GEN01    EXEC PGM=ICEGENER                                                   
//SYSIN    DD   DUMMY                                                           
//SYSPRINT INCLUDE MEMBER=$$BETAPN                                             
//STUFF    SET  STUFF=YG                      JUST TO USE THIS VARIABLE         
//SYSPRINT DD   SYSOUT=X                                                       
//* END OF RZ$GEN                                                               
//NULLFILE DD  DSN=CV.G.SENDZG(+1),                                             
//             DISP=(,CATLG,DELETE),                                           
//             DCB=(GDG.MODEL,RECFM=VB,BLKSIZE=6012,LRECL=3004),               
//             SPACE=(CYL,(5,1),RLSE)                                           
//SYSUT1   DD  DSN=CV.G.SENDZG,                                                 
//             DISP=(OLD,DELETE,KEEP)                                           
//SYSUT2   DD  DSN=YG.G.PVZ.VZFFZO(+1),                                         
//             DISP=(,CATLG,DELETE),                                           
//             DCB=(GDG.MODEL,RECFM=VB,BLKSIZE=6012,LRECL=3004),               
//             SPACE=(CYL,(12,1),RLSE)
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enrico-sorichetti

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Location: italy

PostPosted: Thu Nov 09, 2017 12:36 am    Post subject: Reply to: NULLFILE on ICEGENER Utility
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IIRC a IEBGENER/ICEGENR with no SYSIN should copy SYSUT1 to SYSUT2

the NULLFILE dd will simply allocate a new generation of CV.G.SENDZG
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Robert Sample

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Location: East Dubuque, Illinois, USA

PostPosted: Thu Nov 09, 2017 1:37 am    Post subject:
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Quote:
therefore its will do nothing on SYSUT1 and SYSUT2.
This is not right. IEBGENER / ICEGENER will copy SYSUT1 to SYSUT2 by default; the lack of SYSIN will not impact that.

My interpretation is that the job is using NULLFILE to ensure there is at least one generation of CV.G.SENDZG so the DELETE has something to delete, no matter what. Once the step completes, CV.G.SENDZG will have no generations while YG.G.PVZ.VZFFZO will have one additional generation.
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Ashishpanpaliya

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PostPosted: Thu Nov 09, 2017 6:37 pm    Post subject:
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Thanks Robert. I think your interpretation makes sense.
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Nic Clouston

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Location: UK

PostPosted: Fri Nov 10, 2017 3:11 pm    Post subject:
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If my thinking is correct (big IF!) the method used works because the +1 is not actually catalogued until the end of the step so it will not be included in the SYSUT1 concatenation. On the downside, NULLFILE is not a DDNAME known to ICEGENER so the +1 is not opened and closed so it will have 5 cylinders of whatever data was at that place on disk before (a problem we encountered many moons ago after which the rule was to ALWAYS open and close new data sets even if they are not being written to.

By the way, that is an attrocious block size for SYSUT2.
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enrico-sorichetti

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PostPosted: Fri Nov 10, 2017 4:40 pm    Post subject: Reply to: NULLFILE on ICEGENER Utility
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I might be blatantly wrong but ...

IIRC from some level of SMS/zOS allocation will write an end of file

IMO the setup relies on too many assumptions ...

that the system will write an end of file at allocation
that the generation will be processed in the last defined -first processed order
(not to be caught in the empty dataset in the middle of the concatenation issue )

if all that stands the jcl can be rerun as is with no JCL errors
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