Solution : https://service.sap.com/sap/support/notes/742950 (SAP Service marketplace login required)
Key words : 
46c          sapkb46c52                      46d          sapkb46d43                      610          sapkb61046                      620          sapkb62058                      640          sapkb64016                      700          sapkb70006, oracle database version 9l, oracle cost based optimizer, inbound queue performance reason, cost based optimizer, oracle database version, terms oracle performance, rows' abap statement, system incorrectly accesses, convert database settings
Related Notes : 
       
| 1118297 | XI runtime: QRFC processing of messages | 
| 1040744 | Conntrans Performance Overview | 
| 932975 | Oracle statistics for RFC tables | 
| 756335 | Statistics in tables w/ heavily fluctuating volumes of data | 
| 744869 | Optimizing the performance of inbound scheduler | 
| 683459 | qRFC performance improvements in the inbound scheduler | 
| 601721 | Supplement 11 for qRFC in 3.x,4.x, 6.10, 6.20 and 6.40 | 
| 435125 | Poor performance of tables used by CRM (Oracle only) | 
| 407125 | Poor performance of Q and TRFC on ORACLE | 
| 176754 | Problems with CBO and RBO | 
| 122718 | CBO: Tables with special treatment |