In this blog I will show you the importance of archive and no-archive log mode. Mode of Logging There are two types of logging modes in Oracle database :- 1. ARCHIVELOG :- In this type of logging whatever oracle writes in a redo log file related to transactions in database, saved to another location after a log file has been filled . This location is called Archive location. if database is in Archive log mode then in case of any disaster, we can recover our database upto the last commit and user don’t have to reenter their data. Until a redo log file is not written to the Archive location it cannot be reused by oracle to write redo related data. 2. NOARCHIVELOG :- In this type of logging whatever oracle writes in a redo log file related to transactions in database must be overwritten when all the log files have been filled. In this type of logging we can recover our database upto the last consistent backup we have with us, after that users have to reenter their data. How to check log mode in Oracle database 11g :-

[cognos@rac1 u02]$ sqlplus SQL*Plus: Release 11.2.0.1.0 Production on Thu Oct 25 23:03:44 2012 Copyright (c) 1982, 2009, Oracle. All rights reserved. Enter user-name: /as sysdba Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 – Production

With the Partitioning, Automatic Storage Management, OLAP, Data Mining and Real Application Testing options SQL> archive log list Database log mode No Archive Mode Automatic archival Disabled Archive destination /backup/orcl/

Oldest online log sequence 1 Current log sequence 1 SQL> select name,log_mode from v$database; NAME LOG_MODE ——— – ———– ORCL NOARCHIVELOG

Currently the ORCL database is in NOARCHIVELOG mode To change the Oracle database in ARCHIVELOG mode. PFB below mentioned steps:- 1. If needed set the archive log destination where you want to save your archive logs whether to a single location or to multiple location. If this is not set then Oracle save archive log files in DB_RECOVERY_FILE_DEST location if set. If you have not set your DB_RECOVERY_FILE_DEST location then you have to set your archive location before changing your database to ARCHIVELOG mode. System altered. Note — To change this parameter while database is open, your database has to run with SPFILE, if running through PFILE then shut down your database and make changes in your PFILE and then start the database in MOUNT mode using that changed PFILE

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SQL> alter system set log_archive_dest_1='LOCATION=/u02/archive' scope=spfile;

2. After this you need to shut down your database and start again in MOUNT mode SQL> shu immediate; Database closed. Database dismounted. ORACLE instance shut down. SQL> startup mount;

ORACLE instance started. Total System Global Area 1025298432 bytes Fixed Size 1341000 bytes Variable Size 322963896 bytes Database Buffers 696254464 bytes Redo Buffers 4739072 bytes

Database mounted. 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/archive Oldest online log sequence 1 Next log sequence to archive 1 Current log sequence 1

SQL> select name,log_mode from v$database; NAME LOG_MODE ——— ———— ORCL ARCHIVELOG Database changed to ARCHIVELOG mode. Note :- After you changed your database to ARCHIVELOG mode, take a backup of your database immediately because in recovery scenarios you can recover your database from the last backup taken in this mode.

############################################################################# To change the Oracle database in NOARCHIVELOG mode. PFB below mentioned steps:- 1.Shutdown your running database. SQL> shu immediate Database closed. Database dismounted.

ORACLE instance shut down. 2. Start your database in MOUNT mode. SQL> startup mount ORACLE instance started. Total System Global Area 1025298432 bytes Fixed Size 1341000 bytes

Variable Size 322963896 bytes Database Buffers 696254464 bytes Redo Buffers 4739072 bytes Database mounted. 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/archive

Oldest online log sequence 1 Current log sequence 1 SQL> select name,log_mode from v$database; NAME LOG_MODE ——— ———— ORCL NOARCHIVELOG