Solution : https://service.sap.com/sap/support/notes/435125 (SAP Service marketplace login required)
Key words : 
transaction st04 'reads / user calls', specific sql statements 'bgets/exec', crm mobile scenario arfcrstate, medium sized installations, large installations daily, tables degenerate quickly, 'bgets/row', crm system, crm increase, tables include
Related Notes : 
       
| 771929 | FAQ: Index fragmentation | 
| 742950 | Performance affected on Oracle DB with Supplement 11 | 
| 407125 | Poor performance of Q and TRFC on ORACLE | 
| 375566 | Large number of entries in tRFC and qRFC tables | 
| 332677 | Rebuilding fragmented indexes |