Solution : https://service.sap.com/sap/support/notes/567746 (SAP Service marketplace login required)
Key words : 
current reporting agent preliminary calculationnote 779123, sap service marketplace alias bw, hierarchy-table-buffer-sizenote 748623, long html load times, sap service marketplace, current support package, reporting agent precalculationnote 670780, fact table viewnote 189150, deactivating/activating usage, -cumulatv key figrs
Related Notes : 
       
| 852700 | Performance issues with Excel Calculations in the Analyzer | 
| 838866 | REC: Memory requirement for logical database too large | 
| 825396 | Performance in reports with many selections | 
| 790664 | Analysis of current Reporting Agent preliminary calculation | 
| 779123 | Memory-related terminations at runtime | 
| 764394 | Guide for performance improvement of Web Applications | 
| 748623 | Input help (F4) has a very long runtime - recommendations | 
| 745641 | Memory-related terminations in Reporting Agent pre-calc. | 
| 670780 | Pre-calculating Web templates: Out of Memory problems | 
| 630500 | Maximum size of the interim result with Multiprovider | 
| 629541 | Multiprovider: Parallel Processing | 
| 607164 | MultiProvider: Sequential processing is faster than parallel | 
| 599270 | Portal Content performance - composite SAP Note | 
| 597959 | Portal content performance on EP 5.0 SP 6 - Sammelhinweis | 
| 584216 | RSADMIN parameter for hierarchy table buffer size | 
| 581079 | Performance for the F4 help of navigation attributes | 
| 569584 | BW Business Packages - Installation Guide | 
| 568844 | Very long HTML load times (compared with Analyzer) | 
| 561961 | Deactivating/activating usage of fact table view | 
| 561792 | Client-sided caching of image/gif files | 
| 560255 | Document display performance with large structures | 
| 557870 | FAQ: BW Query Performance | 
| 553084 | Web application is slow, icons are displayed with delay | 
| 550669 | Compressed transfer of BW Web Applications | 
| 542576 | HTTP compression not active | 
| 449477 | Switching the MultiProvider from "parallel" to "sequential" | 
| 402469 | Additional indexes on Master Data Tables | 
| 189150 | Calc. non-cumulatv key figrs before aggreg. | 
| 166551 | Diagnosing storage problems | 
| 161053 | Using SAPGUI in WAN | 
| 130696 | Performance trace in BW |