Understanding ARCHIVELOG and NOARCHIVELOG Modes in Oracle Database

In Oracle Database, ARCHIVELOG and NOARCHIVELOG modes are critical configurations that impact how redo logs are handled once they are filled. Let’s explore both modes and their appropriate use cases.

ARCHIVELOG Mode

In ARCHIVELOG mode, filled redo log groups are not overwritten right away. Instead, the system follows a structured approach:

• Archiving Redo Logs: After a redo log group is filled, it is automatically copied to an archive location.
• Archived Redo Log Files: These filled redo logs are saved as archived redo log files.
• Full Database Recovery: These archived logs are essential for performing full database recovery in the event of a failure.
• High Availability: Ideal for databases that require high availability and strong protection against media failures.
• Online Backups: Enables online backups of the database while it’s running.
• Point-in-Time Recovery: Supports recovery up to the most recent failure, ensuring minimal data loss.
• Additional Storage Requirement: Requires extra disk space to store the archived redo logs.

To check the current log mode of the database, use:

SELECT LOG_MODE FROM V$DATABASE;

To enable ARCHIVELOG mode:

ALTER DATABASE ARCHIVELOG;

NOARCHIVELOG Mode

On the other hand, NOARCHIVELOG mode operates differently:

• Redo Logs Overwritten: Filled redo log groups are overwritten without being archived.
• No Archived Redo Logs: There are no archived redo logs stored for recovery.
• Limited Protection: The database is only protected from instance failures (e.g., crashes or restarts).
• No Online Backups: Backups cannot be performed while the database is running.
• Limited Recovery: You cannot recover the database to the most recent point of failure.
• Appropriate Use: Best suited for test, development, or cloning environments where full recovery is not necessary.

To switch to NOARCHIVELOG mode:

ALTER DATABASE NOARCHIVELOG;

FORCE LOGGING Mode

In addition to ARCHIVELOG and NOARCHIVELOG modes, Oracle offers FORCE LOGGING mode, which can be activated regardless of the archive mode. FORCE LOGGING ensures that all data-modifying operations are recorded in the redo logs, regardless of the current logging or archiving settings.

To check if FORCE LOGGING is enabled:

SELECT force_logging FROM v$database;

To enable FORCE LOGGING:

ALTER DATABASE FORCE LOGGING;

To disable FORCE LOGGING:

ALTER DATABASE NO FORCE LOGGING;

Conclusion

Choosing between ARCHIVELOG and NOARCHIVELOG modes depends on the specific needs of your database environment, such as recovery requirements, availability, and backup policies. Each mode offers unique characteristics suited for different operational scenarios, ensuring flexibility and control over how your Oracle database handles data protection.