Redo Log Files

Every Oracle database has a set of two or more redo log files. The set of redo log files for a database is collectively referred to as the database's redo log.

The redo log is used to record changes made to data. If, for example, there is a database failure, the redo log is used to recover the database. To protect against a failure involving the redo log itself, Oracle allows a mirrored redo log so that two or more copies of the redo log can be maintained on different disks.

ARCHIVELOG Mode

Operating a database in ARCHIVELOG mode enables the archiving of the online redo log.

The ARCHIVELOG command permits a complete recovery from disk failure as well as instance failure, because all changes made to the database are permanently saved in an archived redo log.

For more information about redo log files and database archiving modes, see the Oracle8i Concepts manual. For information about using the ARCHIVE LOG command, see the "Command Reference" in Chapter 8.

To automatically begin archiving, enter

SQL> ARCHIVE LOG START

To list the details of the current log file being archived, enter

SQL> ARCHIVE LOG LIST

SQL*Plus displays results similar to the following:

Database log mode              Archive Mode 
Automatic archival             Enabled 
Archive destination            /vobs/oracle/dbs/arch 
Oldest online log sequence     221 
Next log sequence to archive   222 
Current log sequence           222