Solution : https://service.sap.com/sap/support/notes/530631 (SAP Service marketplace login required)
Key words : 
multi-level atp solution implement, attached source code corrections, multi-level atp, backorder processing filter, symptom performance, product hierarchy, terms transaction, /sapapo/bopmlatp
Related Notes : 
       
| 609435 | Composite SAP note: Performance in backorder processing | 
| 420598 | Composite SAP Note for GATP performance in APO 3.1 | 
| 375193 | Backorder processing: Composite SAP note on posting |