RE: Dynamic sized multiple occurrence data structure

Mike,

With a web app, you're going to want to leave LR off when you finish
anyway.

So your version that does dynamic allocation multiple times is probably
going to perform worse than a version that does that does the maximum
allocation once.

HTH,

Charles Wilt
--
iSeries Systems Administrator / Developer
Mitsubishi Electric Automotive America
ph: 513-573-4343
fax: 513-398-1121
  

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx 
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Mike Cunningham
Sent: Friday, December 15, 2006 3:23 PM
To: RPG programming on the AS400 / iSeries; rpg400-l@xxxxxxxxxxxxxxxx
Subject: Re: Dynamic sized multiple occurrence data structure

Completely agree with your "don't try to save a few cycles at the
expense of readable code". My main concern was using this in a web app
where the app will open, fill in the structure, send the results and
then close and could be doing that a lot if it gets used as I hope. If
it was an app that ran once or twice a day I would not even 
consider it.
If it gets a couple of hits a minute that might be a different story. 
 
And doesn't OS/400 have to load the entire app when it is started even
if some code pages might later get swapped out if not used? Static
storage size  is 5,206,080 and Program size  is 1,806,336 for this app
and I was concerned about the load time.
 
And in this particular app I actually have an array and a MODS. I load
the array because I then sort the data before loading it into 
the MODS.
Then send the MODS as the results set. I do already keep track of the
number of elements and set the result set size to the actual number of
elements. 

rpg400-l@xxxxxxxxxxxxxxxx 12/15/2006 2:45:41 PM >>>

Hi Mike,

Is there any trick available to create a multiple occurrence data
structure and define the size at run time?

[SNIP]

my application is used as a stored procedure that returns a result

set 

and so I can't use arrays.

The "SET RESULT SET" SQL statement can specify the number of rows to 
return.  For example

      C/exec sql Set Result Sets Array :MYMODS for :COUNT Rows
      C/end-exec

Your program will have to keep track of how many elements 
you've loaded

into the MODS and set the number of rows (in the COUNT variable in my 
example, above) appropriately.

As far as how many occurrences exist in your MODS, I strongly 
recommend

that you allocate all 1000 of them as a normal MODS.  The unusused 
occurrences won't matter.  The amount of memory they occupy won't have
any 
significant impact on the system.

It's possible to base your MODS on a pointer, and allocate 
only as many
as 
you need -- exactly the same way you do it with an array -- 
but there's

really no value to doing so (either with a MODS or an array!) if you
only 
have 1000 elements.

You can hurt the performance of your program, and make a 
program that's

very difficult to maintain, using techniques like this.  Sure, you may

save a few kilobytes or even megabytes of memory, but who the heck
cares 
about that?  The iSeries will store unused portions of your program on

disk, only loading it into memory if nothing else needs the 
memory.  So

the amount of memory you use really doesn't have a sigificant impact. 
Certainly nothing worth the cost of making your program hard to
maintain!!

Even if the memory usage is a problem, big deal.  Buy another 512mb
memory 
module for your system.  What does that cost?  $300 or something?  By 
comparison to the extra days it'll take you to write and debug yoru 
program, and by comparison to the years of extra time maintaining your

program, the cost of an extra memory module is extremely cheap.  Don't

create a maintenance nightmare over a couple of kilobytes!

-- 
Scott Klement  http://www.scottklement.com

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