Solution : https://service.sap.com/sap/support/notes/197749 (SAP Service marketplace login required)
Key words : 
additional key words oracle, line item report, takes extremely long, full table scan, oracle databases, symptom executing, transaction cji3, transaction sm50, runtime analysis, 'explain sql'
Related Notes : 
       
| 401949 | Long validity periods in PS reporting III | 
| 339596 | TIME OUT whn insertng WBS in prjct (ORACLE problem) | 
| 209322 | Problem in ORACLE with initial values IV | 
| 200228 | Performance problems in PS under Oracle | 
| 191689 | Problem in ORACLE with initial values II | 
| 182652 | Long Runtimes in PS Reporting II | 
| 180911 | Problem in ORACLE with initial values |