•
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.
Overview
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
