• Two advantages exist to archiving redo log: • Recovery: A database backup, together with online and archived redo log files can guarantee recovery of all committed transaction. • Backup: Can be performed while the database is open. • By default a database is created in NOARCHIVELOG mode
Archived Redo Log Files • Archiving redo log files is accomplished by ARCn(Aechiver) or manually through SQL statement. • An entry in the control file recording the archive log name, log sequence number, and high and low SCN number is made whenever a redo log is successfully archived. • A filled redo log file cannot be reused until a checkpoint has taken place and redo log file has been backed up the ARCn process. • Archived redo log files can be multiplexed. • Archived redo log files must be maintained by the DBA.
Database Storage Hierarchy
SYSTEM and Non-SYSTEM Tablespaces • SYSTEM tablespace: • Created with the database • Contains the data dictionary • Contains the SYSTEM undo segment • Non-SYSTEM tablespaces: • Separate segments • Ease space administration • Control amount of space allocated to a user