Perfect sense. It's a little technical.
5250 screens showing a list use something called a "subfile".
There are three types of subfiles:
- load all subfile
- expanding subfile
- page at a time subfile
The general user will not be able to tell the difference. You have to
delve into the code to notice a difference.
The exception to the general user rule is if the user tries to roll past
9,999 records. That's the limit on a subfile size. The "page at a time"
subfile takes more coding but doesn't have this limitation.
General programming rule of thumb:
If it's a really small list and will never grow huge (like a list of
states) then a "load all" subfile is ok. Do all the I/O and fill it up.
The user can wait on the I/O for such a small list.
If it could be a long list but less than 9,999 rows then use an expanding
subfile. Only load enough rows to fill a screen. If they roll forward do
more I/O. If they roll back just read from the subfile.
If it could be a long list and likely to go over the 9,999 rows then use
the page at a time subfile. Keep track of where you are at. Clear the
subfile and reload the screen full upon every roll. Forward or back.
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