just checking to see if record exists - SETLL on multi format logical versus individual files

Has anyone experienced the following?

This was a weird problem we have been struggling with for about 2 weeks. This Process is for our Bill of material, where used, replace, deduct quantities, remove zero quantities, etc...

We had a case where we needed to modify almost every bill of material structure we have, I think it was deduct some number of rivets.

We fired off the job in batch, and after about 4 hours, we saw that
we were moving at a snail's pace, job would not finish for about 20 hours...

we found the place where we were bogging down was where we check to see
of a specific part exists in the files. We have 3 bill of material files. We _had_ been using a multi-format logical over the 3 files (this is where we changed the program to GREATLY improve performance). The file was opened for input, as we have other files defined to handle the updates, deletes, and adds.

We would do a SETLL then check to see if we have a %equal condition.

We needed to SETLL on each record format, because we needed to check
different things between different BOM files if we would find a record.

We put the program into interactive debug:
We found that the SETLL on the first format went very fast. Record was not found (the manual says that the file cursor goes to eof).
We found that the next SETLL on the second format, and the third format
took about 2 SECONDS longer than the first.

we first thought we had some sort of overide problem, since we had many
layers of member overides, and library overides to get just the data set
we wanted, but we couldn't get anything performing better...

We then removed the multi-format logical file, and instead defined each
file on its own. The process now performs fine.

I am guessing that there is some type of overhead in getting the file
cursor to each different physical file in a multi-format logical that
was eating up CPU cycles, but I'm not sure what...