In a database system, the archive log refers to a copy of a redo log file that has been filled with data and then archived (backed up) to a storage location, such as a separate disk or tape. The redo log files store a record of changes made to the database, and these changes are essential for recovering the database in the event of a failure or for performing certain types of backups (e.g., hot backups).
Here's a brief overview of how archive logs work in Oracle Database:
1. Redo Log Files: When changes are made to the database, they are first written to the redo log files in a circular fashion. These files are crucial for maintaining a record of all transactions that modify the database.
2. Log Switch: Once a redo log file is filled with data, a log switch occurs, and the database starts writing to a new redo log file. The filled redo log file is now ready for archiving.
3. Archiving: The filled redo log file is copied (archived) to a separate location known as the archive log destination. This process ensures that a copy of the redo log is preserved even after a log switch, which helps in data recovery and backup operations.
4. Backup and Recovery: By regularly archiving the redo logs, database administrators can use them to recover the database to a specific point in time in case of a system failure or data corruption. Additionally, archive logs are necessary for performing consistent backups while the database remains operational (hot backups).
It's essential to manage archive logs properly to avoid running out of disk space and to ensure database recoverability. Administrators often set up proper archiving policies and regularly back up archived logs to free up space and safeguard critical data.
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