Solution : https://service.sap.com/sap/support/notes/160063 (SAP Service marketplace login required)
Key words : 
sap/oracle customer systems, load-dependent tuning, rule-based optimizer, cost-based optimizer, profile parameter reason, including oracle support, database parameters ensures, oracle 8 database, oracle performance, parameter setting
Related Notes : 
       
| 618868 | FAQ: Oracle performance | 
| 320540 | Oracle param. no longer supported as of Vers. 8.1 | 
| 215917 | Easy change from Rule to Cost-Based Optimizer | 
| 184134 | Current patch set for Oracle 8.0.6 | 
| 124361 | Oracle parameterization (R/3 >= 4.x, Oracle 8.x/9.x) |