Enabling ARCHIVELOG Mode

Most of the High Availability features of Oracle require you to enable ARCHIVELOG mode for your database. When you enable this mode redo logs will be archived instead of overwritten. The archivelogs are stored in a seperate place usually can backed up regularly by your standard filesystem backup system (NetBackup or whatever). Archive logs are utilized by RMAN, Data Guard, Flashback and many others.

If your going to enable archivelog mode on a real database thats important to you, I would recommend shutting down the database and doing a cold backup just in case. Keeping a "final noarchivelog mode backup" seems to be a good and excepted practice.

Enabling archive mode is simple, just connect to your database in mounted but closed mode (startup mount) and alter the database. But if you don't tune a little you'll run into problems down the road, so lets specify some parameters too. Namely, consider LOG_ARCHIVE_DEST.

Lets start by checking the current archive mode.


SQL> SELECT LOG_MODE FROM SYS.V$DATABASE;

LOG_MODE
------------
NOARCHIVELOG

So we're in NOARCHIVELOG mode and we need to change. We can use a database alter statement, but that won't be perminant, so lets just update the pfile directly. The pfile should be in either $ORACLE_BASE/admin/SID/pfile or $ORACLE_HOME/admin/SID/pfile. I'll add the following lines to the end of the file:


############################
# Archive Log Destinations -benr(10/15/04)
############################
log_archive_dest='/u02/oradata/cuddle/archive'
log_archive_start=TRUE


If we are using SPFILE then use the alter database option

alter database set log_archive_dest='/u02/oradata/cuddle/archive' scope=spfile
alter database set log_archive_start=TRUE scope=spfile




Note that we're not actually required to specify the location of the log destination, but if you don't it'll end up in strange places (in my test it went to $ORACLE_HOME/dbs making a mess). You can specify as many as 10 diffrent archive log destinations by using the paramters log_archive_dest_1 through log_archive_dest_10. Remember, if you run out of space in your archive log destination the database will shut down!

The file location is case sensitive!!!

Now we can startup the database in mount mode and put it in archivelog mode.


$sqlplus / as sysdba;
SQL*Plus: Release 10.1.0.2.0 - Production on Fri Oct 15 16:00:58 2004
Copyright (c) 1982, 2004, Oracle. All rights reserved.
Connected to an idle instance.

SQL> startup mount
ORACLE instance started.

Total System Global Area 184549376 bytes
Fixed Size 1300928 bytes
Variable Size 157820480 bytes
Database Buffers 25165824 bytes
Redo Buffers 262144 bytes
Database mounted.

SQL> alter database archivelog;
Database altered.

SQL> alter database open;
Database altered.