Brief Introduction to definition of archive mode in Oracle

I. Check whether the Oracle database is in archive mode:
1. select name, log_mode from v $ database;
NAME LOG_MODE
------------------------------------------
QUERY NOARCHIVELOG
2. Use the archive log list Command
Database log mode No Archive Mode
Automatic archival Disabled
Archive destination/data/oracle/product/10.2.0/db_1/dbs/arch
Oldest online log sequence 739
Current log sequence 741

II. What is the Oracle archiving mode?
The Oracle database has a redo log of the connected machine. This log records changes made to the database, such as insertion, deletion, and data update. All these operations are recorded in the online redo log. Generally, a database must have at least two online redo log groups. When an online redo log group is full, log switching occurs. At this time, online redo log group 2 becomes the currently used log. When online redo log group 2 is full, log switching occurs again. Write online redo log group 1, and then repeat it.
If the database is in non-archive mode, online logs are discarded during Switching. In archive mode, logs are archived When switching. For example, currently online redo log 1 is used. When 1 is full, log switching occurs and online redo log 2 is started, at this time, the content of online redo log 1 will be copied to another specified directory. This directory is called the archive directory, and the copied file is called the archive redo log.
You can perform catastrophic recovery only when the database is running in archive mode.
1. Differences between the archive log mode and the non-archive log Mode
In non-archive mode, only cold backup can be performed, and only full backup can be performed during recovery. data during the last full backup to system error cannot be recovered.
Archive mode supports hot backup, Incremental backup, and partial recovery.
You can use archive log list to check whether the ARCHIVE mode is not the ARCHIVE mode when the ARCHIVE mode is in the status.

3. Configure the database archive Mode

Change non-archive mode to archive mode:
1) SQL> SHUTDOWN NORMAL/IMMEDIATE;
2) SQL> START MOUNT;
3) SQL> ALTER DATABASE ARCHIVELOG;
4) SQL> ALTER DATABASE OPEN;

5) SQL> make a full backup because the backup logs generated in non-archive log mode are no longer available in archive mode. This step is not very important!

Change archive mode to non-archive mode:
1) SQL> SHUTDOWN NORMAL/IMMEDIATE;
2) SQL> START MOUNT;
3) SQL> ALTER DATABASE NOARCHIVELOG;
4) SQL> ALTER DATABASE OPEN;

3. Enable automatic archiving: LOG_ARCHIVE_START = TRUE
In archive mode, the log file group cannot be overwritten. When the log file is full, if no manual archiving is performed, the system suspends until the archiving is complete.
At this time, you can only read but not write.
Close and restart the archiving log process during running
SQL> ARCHIVE LOG STOP
SQL> ARCHIVE LOG START

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