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Benefits of removing DISPLAY statements

 
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mkk157

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Joined: 17 May 2006
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PostPosted: Thu Aug 13, 2015 12:38 pm    Post subject: Benefits of removing DISPLAY statements
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Hi All,

I completely agree that DISPLAY statements are very helpful in debugging in case of failures. But keeping DISPLAY statements for every record we read from VSAM Master files is not a good practice.

One of my program has a DISPLAY statement in it which gets processed for 250,000 times and prints values on SYSOUT each time. Program used by a Daily job.

I don't see much difference in CPU usage in running the program with and without DISPLAY statements.

What are the other benefits I will get in terms of cost savings ?
As programs DISPLAYS unnecessary information on SYSOUT that spreads for 250,000 lines, When I remove the DISPLAYS I will save some space. how to calculate it ?

Numbering internationalised
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Garry Carroll

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PostPosted: Thu Aug 13, 2015 1:02 pm    Post subject:
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The benefit is in saving spool space.

To see what the space saving would be, maybe try directing SYSOUT to a dataset and see how much space that uses - you'll have to allow for any non-DISPLAY data written to SYSOUT.

Garry
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mkk157

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PostPosted: Thu Aug 13, 2015 2:07 pm    Post subject:
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@Garry Carroll,
thank you. I will write the spool to a file and estimate the space .

Let's see if there are any other benefits with it.
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Bill Woodger

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PostPosted: Thu Aug 13, 2015 2:25 pm    Post subject: Reply to: Benefits of removing DISPLAY statements
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I'm not a big advocate of "whack in some DISPLAYs and see". I'm not even a very small advocate of that.

However, don't even consider taking them out without testing.

One reason I don't like the DISPLAY for "debugging" is that it changes the code, and on occasion that "hides" a problem.

Another reason is that the DISPLAY, for numeric fields, is not always showing you what is actually in the field, such that you may miss a problem simply because the DISPLAY is "lying" to you.

The way to deal with numerics is to MOVE them to numeric-edited items and then DISPLAY that. Do people do that? Not very much.

Another reason is that if you have 250,000 "useless" DISPLAYs, it is "difficult" to spot one meaningful DISPLAY, because it is one amongst 250,000.

Another reason is making the program smaller, and removing non-business requirement "noise".

Another reason is 250,000 is one thing, if you have a Big Fat Loop at some point, you risk filling the spool and making yourself somewhat unpopular.

Etc.

Take them out, but test it.
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PeterHolland

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PostPosted: Thu Aug 13, 2015 3:18 pm    Post subject:
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What is 2,50,000 lines? 250.000? or 2.500.000?

And why is there not a JES2 limit for sysout?
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Marso

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PostPosted: Thu Aug 13, 2015 4:58 pm    Post subject:
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PeterHolland wrote:
What is 2,50,000 lines? 250.000? or 2.500.000?
That's a bit confusing, but this is the way the Indian numbering system works.
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Robert Sample

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PostPosted: Thu Aug 13, 2015 6:20 pm    Post subject:
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Quote:
I don't see much difference in CPU usage in running the program with and without DISPLAY statements.
You won't. The current generation of mainframes can execute many, many, many millions of lines of COBOL for each second of CPU time. So removing 250,000 DISPLAY statements won't have much of a CPU impact.

The cost savings, if that is how you are attempting to justify doing this, probably won't be enough to justify doing it. SYSOUT goes to the JES spool (JES2 or JES3), which is pre-allocated and sized by your system support group to handle the entire site. Removing 250,000 DISPLAY statements may allow some other job to use that spool space -- but if your site is that tight on spool space, you'd be running into major issues getting work completed.

The best justification for this is to remove the annoyance factor of not having to see 250,000 lines of output every day. That would be worth quite a bit to me. And if you do get rid of the DISPLAY statement, don't delete them from the code -- change them to comments or debug statements instead by putting an * or a D in column 7!
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Terry Heinze

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PostPosted: Thu Aug 13, 2015 6:43 pm    Post subject:
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As Robert alluded to, I like to use the "with debugging mode" option of SOURCE-COMPUTER to turn displays on and off. It does require a recompile though.
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steve-myers

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PostPosted: Thu Aug 13, 2015 7:27 pm    Post subject:
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PeterHolland wrote:
What is 2,50,000 lines? 250.000? or 2.500.000?

And why is there not a JES2 limit for sysout?
Some production shops rig production jobs to have unlimited - or at least very large - SYSOUT limits. I'm inclined to agree with Mr. Sample: the hassle factor of getting rid of the debug output is worth the effort to recertify the program.

It's not necessarily just a JES2 issue, too. Sometimes this output is intercepted by SYSOUT archivers, so it's less space required there. It seems kind of dumb to hang onto debug output for 7 years - or whatever the shop standard is!
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PeterHolland

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PostPosted: Thu Aug 13, 2015 8:43 pm    Post subject:
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Well Marso,
Quote:
That's a bit confusing, but this is the way the Indian numbering system works.
I don't really care about Indian numberings. International numbering is what is important. Maybe they are using sanskrit keyboards etc., then i have a hebrew keyboard.
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jerryte

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PostPosted: Thu Aug 13, 2015 11:54 pm    Post subject:
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Consider using
Code:
DISPLAY something UPON SYSPUNCH
to display a status message to a separate dd SYSPUNCH. It has the added bonus of putting the program name in column 73. This can be sent to sysout which allows you to see the status of a program while it is running.
Another option is to use a counter and display only for every 1000th record
Code:
ADD 1 TO WS-DISPLAY-COUNT
IF WS-DISPLAY-COUNT = 1000 THEN
  DISPLAY something
  MOVE 0 TO WS-DISPLAY-COUNT
END-IF
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Bill Woodger

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PostPosted: Fri Aug 14, 2015 1:14 am    Post subject: Reply to: Benefits of removing DISPLAY statements
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That's a nice tip, Jerryte, thanks. I didn't know that.

Anyway, for the topic, junk the DISPLAYs, don't leave them lying around to confuse the code (comments or D in the indicator column, column seven). Remember, they were what someone thought would be useful for some purpose at some time. They may not be, they may be wrong, they may be misleading. They may/will lead you astray one time.

If you feel the overwhelming urge to put DISPLAYs in, think about what you really need, format numeric items, or display the stuff in hex (use the search link about to look for BBHEXD).
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PeterHolland

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PostPosted: Fri Aug 14, 2015 2:14 pm    Post subject:
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The place I worked had a special sysout class (SYSOUT=0) that automatically was purged.
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Nic Clouston

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PostPosted: Fri Aug 14, 2015 4:13 pm    Post subject:
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Places I have worked do not allow debugging DISPLAYS to be active in production code. A change would get bounced if they were found.
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mkk157

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PostPosted: Fri Aug 14, 2015 5:12 pm    Post subject:
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Hi All,
Lots of valuable points shared here. Thank you.

Moderators,
Thanks for correcting the Indian number system to International icon_biggrin.gif

@Bill Woodger,
All the 250,000 DISPLAY statements are useless and does not serve any purpose. There is another DISPLAY statement in place for Error Handling.

@PeterHolland, @Marso, It's Indian Number system.

@Robert Sample, Yes, I will only comment out the unwanted DISPLAYs.

@PeterHolland, SYSOUT =0 I will try it out. But this will purge even the useful messages as well.
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Akatsukami

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PostPosted: Fri Aug 14, 2015 6:01 pm    Post subject:
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mkk157 wrote:
@PeterHolland, SYSOUT =0 I will try it out. But this will purge even the useful messages as well.

Note that this is specific to Mr. Holland's machine. As sysout classes are wholly arbitrary, you must ask your support workgroup what, if anything, is the equivalent in your shop.
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Marso

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PostPosted: Sat Aug 15, 2015 1:23 pm    Post subject:
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If you don't mind doing the I/O and not seeing the result, you can also:

Add a CBL statement right before the ID DIVISION:
Code:
 CBL OUTDD(SYS099)


Use the UPON parameter:
Code:
    DISPLAY UPON SYSLIST


Then have a DD for this logical unit, assigned to SYSOUT or DUMMY, according to your need.
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jerryte

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PostPosted: Mon Aug 17, 2015 7:56 pm    Post subject:
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The OUTDD(ddname) compiler option will change where a regular DISPLAY statement is written to instead of the default SYSOUT dd.

Version 4 of Enterprise COBOL seems to allow a
Code:
DISPLAY something UPON SYSLIST
I have not tried it yet.
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