Summary
Symptom
noarchivelog
Solution
The Oracle database can run in one of two modes: NOARCHIVELOG mode and ARCHIVELOG mode.
On ARCHIVELOG mode the filled online redo log files are archived before they are reused.
On NOARCHIVELOG mode the filled online redo log files are NOT archived.
The redo log is a set of files that protect modified data in memory that has not been written to the datafiles. The redo log can consist of two parts: the online redo log and the archived redo log. The online redo log is a set of two or more online redo log files that record all changes made to the database, including both uncommitted and committed changes. Redo entries are temporarily stored in redo log buffers of the system global area, and then they are written sequentially to an online redo log file. See note 793113 for an indication on where to place this files.
In ARCHIVELOG mode, the database can be completely recovered from both instance and media failure using the ( archived ) redo log files. You can also perform an incomplete recovery of the database. The database can be backed up while it is open and available for use. However, additional administrative operations are required to maintain the archived redo log.
Under very specific circunstances archivelog might be benefitial( Euro changeover, client copies, reorganizations ... ) because no archived redo log is created, no extra work is required by the database administrator. A backup must be taken before and after this operations are performed.
SAP does NOT support the NOARCHIVELOG mode during normal production operation.
If the database operates in NOARCHIVELOG mode, the database can ONLY be completely recovered from instance failure but not from media failure. This means that, in case of media failure you will lose all work done after the last valid offline backup. The database can be backed up only while it is completely closed.
In order to be able to perform a complete or point in time recovery ALL archive log files must be available, therefore it is necessary to back up those files. Please check note 540434 for the absolutly necessary activities.
You can run into several problems:
There are several options:
SELECT LOG_MODE FROM V$DATABASE;
or with
ARCHIVE LOG LIST
There are several oracle parameters that you have to set before changing to ARCHIVELOG mode:
/oracle/<SID>/saparch ( old releases )
/oracle/<SID>/oraarch ( newer releases )
The typical value is for this parameter is:
log_archive_dest = <directory>/<file prefix>
Where <file prefix> is <ORACLE_SID>arch. Note that this is the prefix for the offline redo log file names, not a subdirectory name.
After setting the mentioned parameters you have to follow this steps:
Shutdown the database
Backup the database. This backup can be used with the archive logs that you will generate.
Check that the LOG_ARCHIVE_DEST exist and has enough free space.
Startup mount the database ( do not open )
Switch the database's archiving mode with the command
ALTER DATABASE ARCHIVELOG;
Open the database.
Check that the database is in ARCHIVELOG mode with the commands previosly seen.
Add the archived logs to your backup strategy.
You can also use BRTOOLS to change from NOARCHIVELOG to ARCHIVELOG mode.
Header Data
Affected Releases
Release-Independent
Related Notes
|
Note 863417 - FAQ: Database Archive modes and redo logs
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