Enable/Disable Archive Log Mode 10g/11g

Enable Archive Log Mode
The following are the steps required to enable archive log mode on an Oracle 10g or 11g database.
Verify the database log mode.
[oracle@ora1 ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.1.0 Production on Thu Apr 8 12:02:52 2010
Copyright (c) 1982, 2009, Oracle. All rights reserved.
Connected
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> archive log list
Database log mode No Archive Mode
Automatic archival
Disabled
Archive destination USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence 25
Current log sequence 27
SQL>

The log mode is No Archive Mode. Note that Archive destination is USE_DB_RECOVERY_FILE_DEST. You can determine the path by looking at the parameter RECOVERY_FILE_DEST.

SQL> show parameter recovery_file_dest
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest string /u01/app/oracle/flash_recovery_area
db_recovery_file_dest_size big integer 3852M
SQL>


By default, archive logs will be written to the flash recovery area. If you do not want to write archive logs to the flash recovery area you can set the parameter LOG_ARCHIVE_DEST_n to the location in which you wish to write archive logs.

SQL> alter system set log_archive_dest_1='LOCATION=/u02/app/oracle/oradata/orcl/arch' scope = both;
System altered.
SQL> archive log list;
Database log mode No Archive Mode
Automatic archival Disabled
Archive destination /u02/app/oracle/oradata/orcl/arch
Oldest online log sequence 25
Current log sequence 27
SQL>


Now we shutdown the database and bring it backup in mount mode.
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
 Total System Global Area  849530880 bytes
Fixed Size                  1339824 bytes
Variable Size             511708752 bytes
Database Buffers          331350016 bytes
Redo Buffers                5132288 bytes
Database mounted.
SQL>
Lastly all that is needed it set archive log mode and open the database.
SQL> alter database archivelog;
 Database altered.
 SQL> alter database open;
 Database altered.
 SQL> archive log list
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /u02/app/oracle/oradata/orcl/arch
Oldest online log sequence     25
Next log sequence to archive   27
Current log sequence           27
SQL>


We can now see that archive log mode is enabled. Notice that Automatic archive is enabled as well. In Oracle 9i an earlier another parameter needed to be set in order to enable automatic archiving. This in no longer the case in 10g and 11g as automatic archiving is enabled when the database is placed in archive log mode.
You can switch to the log file to see that an archive is written to archive log location.
SQL> alter system switch logfile;
 System altered.
 SQL> host
[oracle@ora1 ~]$ ls /u02/app/oracle/oradata/orcl/arch
1_27_711369564.dbf
[oracle@ora1 ~]$ exit
exit
 SQL> 

Disable Archive Log Mode
Note: It is recommended to perform a backup of the database (after a shutdown normal or immediate) prior to changing the archive status of a database.
The following are the steps required to disable archive log mode on an Oracle 10g or 11g database.
Verify the database log mode.
[oracle@ora1 ~]$ sqlplus / as sys<span class="searchterm2">db</span>a
 SQL*Plus: Release 11.2.0.1.0 Production on Thu Apr 8 12:54:05 2010
 Copyright (c) 1982, 2009, Oracle.  All rights reserved.
 Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
 SQL> archive log list;
Database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            /u02/app/oracle/oradata/orcl/arch
Oldest online log sequence     26
Next log sequence to archive   28
Current log sequence           28
SQL>
The Database log mode is Archive mode. Next we shut down the database and bring up back up in mount mode.
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
 Total System Global Area  849530880 bytes
Fixed Size                  1339824 bytes
Variable Size             511708752 bytes
Database Buffers          331350016 bytes
Redo Buffers                5132288 bytes
Database mounted.
SQL>

All that is left is to disable archive log mode and open the database.
SQL> alter database noarchivelog;
 Database altered.
 SQL> alter database open;
 Database altered.
 SQL> archive log list;
Database log mode              No Archive Mode
Automatic archival             Disabled
Archive destination            /u02/app/oracle/oradata/orcl/arch
Oldest online log sequence     26
Current log sequence           28
SQL>

for 9i database
SQL>shutdown immediate;

Edit below parameters in pfile(init.ora) file.

1. LOG_ARCHIVE_START=TRUE

As you can see, ARCHIVELOG mode has been disabled.