When using the EXP utility for export backup or data migration, you may sometimes encounter numerous “EXP-00091: Exporting questionable statistics” errors.
How to Fix:
Set the Linux system NLS_LANG environment variable to the database character set.
1) Query the database character set (one of many methods)
SQL> select userenv('language') from dual;
USERENV('LANGUAGE')
—————————————————-
AMERICAN_AMERICA.AL32UTF8
2) Set the NLS_LANG environment variable on the Linux operating system
export NLS_LANG=AMERICAN_AMERICA.AL32UTF8
Done. After this fix, you will no longer see this error when performing EXP export operations.