[理论]undo有关的4个参数:transactions_per_rollback_segment,undo_retention,_highthreshold_undoretention,_rollb
SQL>showparameterundoNAME_COL_PLUS_SHOW_PARAMTSTypeVALUE_COL_PLUS_SHOW_PARAM-------------------------------------------------------------------------------------------undo_managementstringAUTOundo_ret