The main reason for running in archivelog mode is that one can
provide 24-hour availability and guarantee complete data
recoverability. It is also necessary to enable ARCHIVELOG mode before one can start to use on-line database backups. To enable ARCHIVELOG
mode, simply change your database startup command script, and
bounce the database:
SQLPLUS> connect sys as sysdba
SQLPLUS> startup mount exclusive;
SQLPLUS> alter database archivelog;
SQLPLUS> archive log start;
SQLPLUS> alter database open;
NOTE1: Remember to take a baseline database backup right after
enabling archivelog mode. Without it one would not be able to recover.
Also, implement an archivelog backup to prevent the archive log
directory from filling-up.
NOTE2: ARCHIVELOG mode was introduced with Oracle V6, and is
essential for database point-in-time recovery. Archiving can be used in
combination with on-line and off-line database backups.
NOTE3: You may want to set the following INIT.ORA parameters when
enabling ARCHIVELOG mode: log_archive_start=TRUE,
log_archive_dest=... and log_archive_format=...
NOTE4: You can change the archive log destination of a database on-
line with the ARCHIVE LOG START TO 'directory'; statement. This
statement is often used to switch archiving between a set of
directories.
NOTE5: When running Oracle Real Application Server (RAC), you need
to shut down all nodes before changing the database to ARCHIVELOG
mode.