Solution : https://service.sap.com/sap/support/notes/114716 (SAP Service marketplace login required)
Key words : 
/3 profile parameter rsdb/max_blocking_factor, additional key words statistics, install oracle patch set 8, oracle profile parameter 'optimizer_index_cost_adj', latest patch set 8, ora parameter db_file_multiblock_read_countand, cost based optimizer, increased network load, ora parameter mentioned, costs calculated originally
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