What part of an RPG program is re-used?

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