SAP Note 18815 - Performance during line item display

Symptom:

Bad performance while displaying line items.
Key words: FBL1 FBL2 FBL3 FBL4 FBL5 RFEPOS00 T021Z

Cause and prerequisites

Use of a line item display variant which requires reading document information for each line item ('Special variant').

Solution
Check, if the line layout variant is defined as desired, or if it contains fields which are not included in the tables BSID BSIK BSIS.
To check with transaction FAKP - choose variant and function 'Usage':
If, for example, the field 'Reread doc.header' has been marked, the variant contains a field from BKPF. That means that for every line that is to be issued the program must read table BKPF.
In such cases please check whether the correct field field was chosen and, if need be, replace it with another field.
(Example: Instead of the document header text BKTXT, you require the segment text for line item SGTXT.)
To check which variants are special variants, you can use transaction SE16 to access table T021Z, listclass '2', mark all fields for output, and check for which variants the program must reread data.