Solution : https://service.sap.com/sap/support/notes/199441 (SAP Service marketplace login required)
Key words : 
substitutions user exits business transaction events, sap delivery solution methods, function 'explain sql statement', frequent problems - check list, customer enhancement                        customer enhancements, additional key words performance, mass processing generates generally, influences customer enhancements, function sql trace, key word 'performance'
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| 128221 | Increased memory consumption with Oracle >8.0.X | 
| 109034 | Collective note: SAPDBA - performance/CBO |