Managing Redo log   «Prev  Next»

Managing Database Redo Log Conclusion

Lesson 8
In this module, you learned how to perform the basic tasks required for managing database redo log files. You should understand how to protect your redo log files by multiplexing them and why that is important. You should also be comfortable performing any of the following tasks:
  1. Listing the redo log files and groups in a database
  2. Creating a new redo log group or a new member within a group
  3. Moving redo log files
  4. Dropping redo log files
  5. Manually forcing a log switch

What Is the Archived Redo Log?

Oracle Database lets you save filled groups of redo log files to one or more offline destinations, known collectively as the archived redo log. The process of turning redo log files into archived redo log files is called archiving. This process is only possible if the database is running in ARCHIVELOG mode. You can choose
  1. automatic or
  2. manual
An archived redo log file is a copy of one of the filled members of a redo log group. It includes the redo entries and the unique log sequence number of the identical member of the redo log group. For example, if you are multiplexing your redo log, and if group 1 contains identical member files a_log1 and b_log1, then the archiver process (ARCn) will archive one of these member files. Should a_log1 become corrupted, then ARCn can still archive the identical b_log1. The archived redo log contains a copy of every group created since you enabled archiving.
When the database is running in ARCHIVELOG mode, the log writer process (LGWR) cannot reuse and hence overwrite a redo log group until it has been archived. The background process ARCn automates archiving operations when automatic archiving is enabled. The database starts multiple archiver processes as needed to ensure that the archiving of filled redo logs does not fall behind.

You can use archived redo logs to:
  1. Recover a database
  2. Update a standby database
  3. Get information about the history of a database using the LogMiner utility


In this module, you were introduced to the following terms:
  1. crash recovery
  2. media recovery
  3. system crash
In the next module, you will learn about archiving redo log files.