Solution : https://service.sap.com/sap/support/notes/132861 (SAP Service marketplace login required)
Key words : 
calculate correct access paths, sapdba command line functions, cost-based optimizer, cost-cased optimizer, operating system level, aforementioned log files, sapdba -analyze dbstatco, symptom system performance, sapdba -checkopt psap%, sapdba -checkopt
Related Notes : 
       
| 766349 | FAQ: Oracle SQL optimization | 
| 618868 | FAQ: Oracle performance | 
| 588668 | FAQ: Database statistics | 
| 403704 | BRCONNECT - Enhanced function for Oracle DBA | 
| 303140 | Techn.object: performance problem f.structure lists | 
| 215917 | Easy change from Rule to Cost-Based Optimizer | 
| 184513 | CBO: Parallel generation of optimizer statistics | 
| 131372 | CBO: Tuning of expensive SQL statements | 
| 118556 | SAPDBA: New ALIAS (DBAORA) and NEWS in the SAPNET | 
| 109034 | Collective note: SAPDBA - performance/CBO | 
| 96296 | CC-ERROR: Database problem in client copy | 
| 93256 | CBO: Changes for installation of 4.0 | 
| 93098 | CBO: Changes in upgrade to 4.0 |