Re: Avoid Level checks was ( Generic RPG File Handler for File I/O using OA)

A small addendum to Charles' comment about sharing access paths. What he
says is true, however there is a caveat: You must create/restore the
widest (meaning longest key field string) first, then any combination of
keys less than that will indeed share the one access path. A restore
within a collection/library does that for you, but if the indexes/LFs are
in different collection/library, you may need to do that manually. For
instance if your key is:

F1, F2, F3, F4, F5
Then a key with: F1, F3, F5 will share that access path.

A key with:
F2, F5, F1 most likely will not share the access path and create a new one
simply because the existing path does not assist in creating the new one.

If your original key was: F1, F4, F5, and you add an index with F2, F1, F3
then it's highly likely that a new access path will be created even though
the F1 might be helpful.

Creating the most efficient indexes and LFs require some detailed thought
about how the data is accessed, not the old S/38 way of "I need a logical,
so I'll just create it" mentality.

One way we fix several types of performance problems is simply to remove
then restore the library allowing the system to sort it out. The restore
message that indicated sharing access paths is the best message you can see
from a performance perspective.

--
Jim Oberholtzer
Chief Technical Architect
Agile Technology Architects


On Wed, Jun 29, 2022 at 8:52 AM Charles Wilt <charles.wilt@xxxxxxxxx> wrote:

On Tue, Jun 28, 2022 at 12:34 AM LOGIC IT: Karl FRITZ <k.fritz@xxxxxxxx>
wrote:

And each new LF requires maintaining of access paths. Have a lot of fun
restoring a huge file with
50 LF's.

No it does not. You can have as many LFs as you want and as long as they
have the same keys, there will be only 1 access path.

In Frank's scenario, where you add a field to the PF and create a new LF
that includes the field for the programs that would need it. 99.9% of the
time, the new LF would have the same keys as existing LFs. So there is no
additional overhead.

Charles
--