RE: user space

thank you and the others on the list for the welcoming speech (really).

there is so much to know about the as400 (we don't have an iSeries yet)
and there are so few people who share their knowledge and less people
i'm able to ask questions. so thanx for the info.

one further question: as far as i understood the userspace object, it is
one piece of memory i could use and not broke down to rows and columns.
so how would one do a fast, keyed lookup?

-----Original Message-----
From: Scott Klement [mailto:klemscot@klements.com] 
Sent: Tuesday, January 21, 2003 5:20 PM
To: RPG programming on the AS400 / iSeries
Subject: Re: user space




On Tue, 21 Jan 2003, Mihael Knezevic wrote:
>
> my first question: is this list only for rpg400 or also for rpg iv 
> (previously named ile rpg) ?
>

This is for all flavors of RPG that run on the iSeries/400 (or AS/400)

> now my second question: would it be better to read the necessary data 
> from the second table into a userspace object?

There are some key differences between a PC and an iSeries/400, which
you may not have considered.

First, you've got many users on the iSeries.   Writing your program to
use
additional resources will almost certainly slow down another user.

The second is that the OS/400 operating system treats both RAM and disk
as one big space. (In other words, a pointer could be used to point to
any place on disk or in a file, directly, aside from the security
considerations) They call this "single level store."

Since it's all treated as one space, the operating system tries to
optimize things by moving disk objects to the RAM portion of storage,
when they're being used, etc.

The idea is that the operating system does all of the optimizations of
pre-loading things and tuning them for performance, etc, so that every
program doesn't have to do it's own optimizing.

That means that there is a very good chance that your second file is
being read from RAM already!

If you really want to second-guess the algorithm, you can try to load
your data into a user space, and maintain some way of doing fast, keyed,
lookups on that space.   (Or better yet, a user-index)   but I think all
you'd succeed in would be making your program more complicated.

Alternatively, if you're really concerned about it, you could do a
SETOBJACC command to force your file to be in RAM (if possible).   But,
in
a way, that's like saying "my program is more important than anyone
elses!" because it means someone elses program won't be able to use the
RAM.

Anyway, these are some things to think about...   hopefully, this
information will prove useful.

Welcome to the community!

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