This section describes how to set the archiving mode of the database and how to control the archiving process. The following topics are discussed:
Setting the Initial Database Archiving Mode
You set the initial archiving mode as part of database creation in the CREATE DATABASE statement. Usually, you can use the default of NOARCHIVELOG mode at database creation because there is no need to archive the redo information generated by that process. After creating the database, decide whether to change the initial archiving mode.
If you specify ARCHIVELOG mode, you must have initialization parameters set that specify the destinations for the archive log files
Changing the Database Archiving Mode
To change the archiving mode of the database, use the ALTER DATABASE statement with the ARCHIVELOG or NOARCHIVELOG clause. To change the archiving mode, you must be connected to the database with administrator privileges (AS SYSDBA).
The following steps switch the database archiving mode from NOARCHIVELOG to ARCHIVELOG:
An open database must first be closed and any associated instances shut down before you can switch the database archiving mode. You cannot change the mode from ARCHIVELOG to NOARCHIVELOG if any datafiles need media recovery.
Before making any major change to a database, always back up the database to protect against any problems. This will be your final backup of the database in NOARCHIVELOG mode and can be used if something goes wrong during the change to ARCHIVELOG mode. See Oracle Database Backup and Recovery Basics for information about taking database backups.
To enable or disable archiving, the database must be mounted but not open.
Changing the database archiving mode updates the control file. After changing the database archiving mode, you must back up all of your database files and control file. Any previous backup is no longer usable because it was taken in NOARCHIVELOG mode.
Performing Manual Archiving
To operate your database in manual archiving mode, follow the procedure shown in"Changing the Database Archiving Mode". However, when you specify the new mode in step 5, use the following statement:ALTER DATABASE ARCHIVELOG MANUAL;
When you operate your database in manual ARCHIVELOG mode, you must archive inactive groups of filled redo log files or your database operation can be temporarily suspended. To archive a filled redo log group manually, connect with administrator privileges. Ensure that the database is mounted but not open. Use the ALTER SYSTEM statement with the ARCHIVE LOG clause to manually archive filled redo log files. The following statement archives all unarchived log files:ALTER SYSTEM ARCHIVE LOG ALL;
When you use manual archiving mode, you cannot specify any standby databases in the archiving destinations.
Even when automatic archiving is enabled, you can use manual archiving for such actions as rearchiving an inactive group of filled redo log members to another location. In this case, it is possible for the instance to reuse the redo log group before you have finished manually archiving, and thereby overwrite the files. If this happens, the database writes an error message to the alert file.
Adjusting the Number of Archiver Processes
The LOG_ARCHIVE_MAX_PROCESSES initialization parameter specifies the number of ARCn processes that the database initially invokes. The default is two processes. There is usually no need specify this initialization parameter or to change its default value, because the database starts additional archiver processes (ARCn) as needed to ensure that the automatic processing of filled redo log files does not fall behind.
However, to avoid any runtime overhead of invoking additional ARCn processes, you can set the LOG _ARCHIVE _MAX_PROCESSES initialization parameter to specify up to ten ARCn processes to be started at instance startup. The LOG _ARCHIVE _ MAX _PROCESSES parameter is dynamic, and can be changed using the ALTER SYSTEM statement. The database must be mounted but not open. The following statement increases (or decreases) the number of ARCn processes currently running:ALTER SYSTEM SET LOG_ARCHIVE_MAX_PROCESSES=3;
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