Oracle 11g 导出报错exp-00091，解决办法。

今天做数据库导出报错：EXP-00091: Exporting questionable statistics.
在对ORACLE数据库做exp备份导出时报EXP-00091: Exporting questionable statistics”错误：详情如下：
EXP-00091: Exporting questionable statistics.
EXP-00091: Exporting questionable statistics.
EXP-00091: Exporting questionable statistics.
. . exporting table test 12 rows exported
EXP-00091: Exporting questionable statistics.
. . exporting table users 129 rows exported
EXP-00091: Exporting questionable statistics.
EXP-00091: Exporting questionable statistics.
EXP-00091: Exporting questionable statistics.
EXP-00091: Exporting questionable statistics.
问题原因：
引起此问题的原因是数据库字符集和操作系统的NLS_LANG不一致导致
处理方法：
查询数据库的字符集信息
SQL> select userenv('language') from dual;

USERENV('LANGUAGE')

AMERICAN_AMERICA.WE8ISO8859P1
设置操作系统的NLS_LANG值
export NLS_LANG=AMERICAN_AMERICA.WE8ISO8859P1
重新运行数据库导出命令
exp system/oracle file='/tmp/full.dmp' full=y;