Solution : https://service.sap.com/sap/support/notes/563608 (SAP Service marketplace login required)
Key words : 
hash index consumes memory space, dnnn table remains small, average exception aggregation, memory consumption reason, 'table standard' type, <g_thx_s> memory table, bw support packages, import support package 7, 0b support package 7, individual key figures
Related Notes : 
       
| 558191 | Too much memory consumption in the OLAP processor | 
| 517950 | SAPBWNews BW 3.0B Support Package 07 |