RE: Affect of program size on memory usage -- RPG400-L

As a general guideline, I would agree that reducing static storage is
desirable. But I feel uncomfortable with that as a blanket statement.
For procedures that are called frequently, using static (or global)
variables could improve performance by eliminating
allocation/initialization for each execution. What's most important for
the developer is to understand how this works, so they can make better
design choices.

I tend to code for clarity, first, leaving optimization for later. That
does not mean that I don't try to be efficient, just that efficiency
comes in second place to quality. Get the right results, then fix
performance issues if needed... Scoping work variables to the proc is a
great way to reduce unneeded complexity, but this is (to me) more a
style issue than a performance issue.

-Eric DeLong

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Alan Campin
Sent: Monday, November 16, 2009 11:30 AM
To: RPG programming on the IBM i / System i
Subject: Re: Affect of program size on memory usage

Coming from IBM the more static storage that a ILE program has the
slower it
is going to run because it has to manage the static storage. The more
stuff
that is automatic, the better it is going to run. ILE programs are very
efficient at allocating and deallocating automatic storage.

Reducing static storage is always a good thing.

On Mon, Nov 16, 2009 at 9:40 AM, DeLong, Eric
<EDeLong@xxxxxxxxxxxxxxx>wrote:

Hi Darren,

I'll take a shot at this... I believe this falls back to how SLS
(single level storage) manages objects. There will only be one copy

the program object in main storage at one time. Potentially many JOBS
can invoke that program object. All memory allocations for that

program

occur at run time, so that storage for this program is local to each

JOB

that is running the program.

The actual size of the program object doesn't impact the system as

much

as the amount of storage to be initialized. Moving static globals to
local may not improve performance, since local variables must be
allocated and initialized each time the procedure is invoked. In the
global/static realm, the allocation only occurs once...

-Eric DeLong

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of darren@xxxxxxxxx
Sent: Monday, November 16, 2009 8:53 AM
To: midrange-RPG RPG message board
Subject: Affect of program size on memory usage

I've taken some pride in reducing static storage by moving variables

local subprocedures, which also makes the code more readable too.
However,
I often see the size of the program itself grow by much more than the
storage reduction. I use DBGVIEW(*LIST), so I'm fairly certain that

I
add more source lines, my program object grows quickly in size. SQL
also
takes a toll as it adds access path information when the program is
first
executed.

My question is, does the system i load the whole program object into
memory, or is their some intelligence there? If so, is there a way to
compare the real program object size, minus the source view?

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