Solution : https://service.sap.com/sap/support/notes/906139 (SAP Service marketplace login required)
Key words : 
partitioned tables separately, dbms_stats calculates local, partitioned tables, lot longer, brconnect reason, prerequisites unlike, analyze command, work involved, bw environment, projected locally
Related Notes : 
       
| 1013912 | FAQ: Oracle BW performance | 
| 806554 | FAQ: I/O-intensive database operations | 
| 706132 | Composite SAP Note: Problems with Oracle 9i |