Solution : https://service.sap.com/sap/support/notes/574349 (SAP Service marketplace login required)
Key words : 
performance problems occur, specific message types, idoc relationship types, partner type ls, generated inbound idoc, local idoc number, outbound idoc number, sender partner type, idoc number, local number
Related Notes : 
       
| 1083694 | IDoc adapter: IDX5 and IDoc tracking | 
| 707820 | Performance: Object links and RSRLDREL | 
| 566765 | Deletion: Reducing read accesses to SRRELROLES | 
| 505608 | ALE: Reorganizing IDOCREL |