Solution : https://service.sap.com/sap/support/notes/817934 (SAP Service marketplace login required)
Key words : 
/offordiagnose optimize improved operator join onin, diagnose optimize aggregation offafter restarting, optimze_operator_join_costfuncdiagnose optimize operator join costfunc, diagnose optimize join parallel <number, diagnose optimize join parallel minsize 100, join_operator_implementationdiagnose optimize operator join, improved join cost function, optimize_fetch_reversediagnose optimize fetch order, diagnose update stat <number>, optimize_join_outerdiagnose optimize join outer
Related Notes : 
       
| 1139904 | FAQ: MaxDB/liveCache kernel parameters | 
| 767635 | MaxDB Version 7.5 parameter settings for OLTP/BW |