What part of an RPG program is re-used?

[Joe Pluta <joepluta@xxxxxxxxxxxxxxxxx>]

Back in the olden days, one of the things that was so efficient about 
the midrange was the way it used a shared, read-only section of memory 
for the program code.  That way, 20 people using order entry would use 
only one copy of the program.  The variables specific to a given job 
were stored in the job itself (in the Process Access Group, if I 
remember correctly).

My question is how much of that still holds today?  Here's what I'm 
wondering about.  I'd like to create a service program that provides 
data from a table.  That table is static; it will not change during the 
life of the job and most likely only needs to be refreshed at IPL.

I could use a database table and pin the table to memory with SETOBJACC, 
but that still means I have to go through a layer of DB management each 
time I want a value.  Unless things have changed drastically, having an 
array in my program will still be faster, especially if I have an 
ordered array with a relatively small number of elements (measured in 
the 100s at most) and then load that table at initialization time.  Even 
if the data is 1K in length, I'm talking less than 1MB of memory.  
However, what I don't want is 100 user jobs to create 100 copies of that 
table; now I'm talking megabytes and as the number of tables and users 
grows, so does the used (duplicated) memory.

So, is there a way to have a static chunk of memory that is shared by 
all the jobs that call this service program?  The program code will 
certainly be shared, but what about the data?  If I create an array in 
my D-specs, as far as I know I can't make it read only.  Therefore it 
has to be in the PAG (or whatever the equivalent is), and thus is 
repeated per job.

The more I look at it, the more it seems that SETOBJACC is my best bet 
and that I have to choose between speed and memory usage.  I suppose I 
can share a single user space among multiple jobs.  Or a user index, 
perhaps?  I always wonder about those sorts of objects, though, since 
every request requires a fully qualified object name.  How often do 
those get resolved?

Thoughts?

Joe