ORA-31693 ORA-01555错误

oracle10g用数据泵导出数据提示，提示错误如下：

ORA-31693: Table data object "SMARTGPS2006"."MCC_ASYN_POS":"MCC_ASYN_POS201409" failed to load/unload and is being skipped due to error:
ORA-29913: error in executing ODCIEXTTABLEPOPULATE callout
ORA-01555: snapshot too old: rollback segment number 21 with name "_SYSSMU21$" too small

解决方法如下：

show  parameter   undo_retention;查看该变量的值

SQL> show  parameter  undo_retention;

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_retention                       integer     900

修改该参数的值：

alter  system  set undo_retention=18000;

show  parameter  undo_retention;