We also had it running slow. After adding a number of custom indexes, it's
flying.
To find the indexes you need, turn debug on the client, capture the select
statements at the time P03B12 is slow, and run them individually against the
as400 in sql (with debug on). The optimizer will then return a list of
suggested indexes. Create the indexes using CREATE INDEX in sql, and finally
delete the sqlpkg's. The new indexes will then kick in.
It's a slow and painful way of finding missing indexes, but it does work.
On the KG, under Knowledge Browser, there's some documents that describe the
above, as well as how to capture missing indexes system wide.