Oracle’s National Language Support (NLS) parameters play a crucial role in determining how your database handles language-specific features like character sets, date formats, and numeric conventions. This guide will help you understand and check your Oracle NLS settings at various levels.
Understanding NLS Parameter Hierarchy
Oracle NLS settings follow a three-tier hierarchy:
- Session Level
- Instance Level
- Database Level
Checking NLS Parameters
1. Session Level Settings
To view current session NLS parameters, use:
SELECT * FROM NLS_SESSION_PARAMETERS;
For specific parameters:
SELECT sys_context('USERENV', 'NLS_DATE_FORMAT') FROM dual;
SELECT sys_context('USERENV', 'NLS_LANGUAGE') FROM dual;
2. Instance Level Settings
Check instance parameters through:
SHOW PARAMETER NLS
3. Database Level Settings
Query database defaults:
SELECT * FROM NLS_DATABASE_PARAMETERS;
Common NLS Parameters
Essential Parameters
- NLS_LANGUAGE: Specifies default language
- NLS_TERRITORY: Sets default territory conventions
- NLS_DATE_FORMAT: Controls date format display
- NLS_TIMESTAMP_FORMAT: Determines timestamp display
- NLS_CHARACTERSET: Defines database character set
- NLS_NCHAR_CHARACTERSET: Sets national character set
Modifying NLS Settings
Temporary Session Changes
ALTER SESSION SET NLS_DATE_FORMAT = 'DD-MON-YYYY';
ALTER SESSION SET NLS_LANGUAGE = 'FRENCH';
Permanent Instance Changes
Add to init.ora or spfile.ora:
NLS_LANGUAGE = AMERICAN
NLS_TERRITORY = AMERICA
Best Practices
- Documentation: Always document NLS settings in your application architecture
- Consistency: Maintain consistent settings across development and production
- Testing: Test applications with various NLS settings
- Monitoring: Regularly audit NLS parameters for unexpected changes
Troubleshooting Tips
Common issues and solutions:
-
Date Format Mismatches
- Verify session NLS_DATE_FORMAT
- Check application date handling code
- Consider explicit TO_DATE conversions
-
Character Set Issues
- Confirm NLS_CHARACTERSET compatibility
- Check for data truncation
- Verify client character set settings
-
Performance Concerns
- Monitor sorting operations
- Review linguistic indexes
- Check for character set conversion overhead
Conclusion
Understanding and properly managing Oracle NLS settings is crucial for maintaining data integrity and application functionality in a global environment. Regular monitoring and documentation of these settings will help prevent unexpected behavior and ensure smooth operation of your Oracle database applications.