Solution : https://service.sap.com/sap/support/notes/592366 (SAP Service marketplace login required)
Key words : 
sm50 displays long processing times, change database parameter rsdb/max_in_blocking_factor, bw-sys-db component, oracle cost based optimizer, im-specific update rules, update infocube 0imfa_1with data, long runtimes occur, full table scan, generated secondary index 917, infocube update
Related Notes : 
       
| 634263 | Selects with FOR ALL ENTRIES | 
| 613858 | BCT-IM: Performance of the 0IM_FA_IP_9 DataSource | 
| 555030 | Deactivating BW-initiated DB statistics | 
| 500966 | Data is missing: Pre-analyzing the problem in the PSA | 
| 460473 | BCT-IM: Performance problems when reading from the PSA | 
| 398041 | INFO: CO-OM/IM-Content (BW) | 
| 328707 | BCT-IM:Performance in InfoCube update for 0IMFA_1 | 
| 316718 | BCT-IM: Preconditions for InfoCube update 0IMFA_1 |