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You are here: Experts > Computing/Technology > Cobol > Cobol > MVS COBOL: DISPLAY STATEMENT PERFORMANCE
Expert: David Nelson
Date: 9/15/2008
Subject: MVS COBOL: DISPLAY STATEMENT PERFORMANCE
Question
I'm analyzing an MVS JCL running some Cobol programs.
This JCL has avarage an elapsed time of 02.44.38 against a CPU time of 00.35.23, with 2725527 Service Units and a Sysout Print Lines of 400,000 (!!!).
The main Cobol programs infact use a lot of DISPLAYs and most of fields displayed are COMP.
My question is (before deciding to write a report file instead of DISPLAYing such a huge numbers of lines):
what the impact could be on the elapsed time if I reduce numbers of DISPALYs (for istance DISPLAYing more fields in one single DISPLAY instead of one DISPLAY by field) and if the fact of DISPLAYing lot of COMP field impact the elapsed time?
tks a lot. Daniele Piras
Answer
If I understand you are saying 35 min 23 sec CPU in 2 hr, 44 min, 38 Secs elapsed!
While this may be affected by the 400,000 lines of sysout display, how is the output blocked? By itself display is fairly efficient, but if the block is very low (BLKSIZE=121,LRECL=121 or close that will slow it down. If you have many separate DISPLAYs for a single input record then definitely combining will help. Display will auto wrap lines at 120 bytes of data, but I suggest keeping display to a non-report data output.
However, you can tell very quickly by looking at the excp count for the various files and what other functions are being used. A quick test would be to '*' the DISPLAY lines and re-run, if a big change then DISPLAY is a problem. If not, then other processing and I/O is the problem. Also, what is the general CPU %busy load. If it is very high (97+%) then your app could just be a victim of no cpu cycles. Your service unit figure is not out of line for 35 min CPU time. If your WAIT time is very large that would account for the long time also.
Your total job time is not out of line for the CPU vs Elapsed.
If you have further questions after you try above, give me some more stats.
David
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