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理解Oracle闪回级别【Oracle闪回技术】（一）-CSDN博客

Oracle默认是不开启闪回数据库的。如果开启闪回数据库的前提条件是，开启Oracle归档模式并启用闪回恢复区。
因为闪回日志文件存放在闪回恢复区中，如果在RAC环境下，必须将闪回恢复区存储在集群文件或者ASM文件中。

一、开启闪回数据库步骤

1.1）####################################################
开启Oracle归档模式
[root@cdp /]# su oracle
[oracle@cdp /]$ sqlplus sys/abcABC123 as sysdba

SQL*Plus: Release 12.2.0.1.0 Production on Wed Apr 24 09:38:26 2024

Copyright (c) 1982, 2016, Oracle.  All rights reserved.

Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

sys@ORCL>shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
sys@ORCL>startup mount;
ORACLE instance started.

Total System Global Area 3221225472 bytes
Fixed Size            8797928 bytes
Variable Size          788529432 bytes
Database Buffers     2415919104 bytes
Redo Buffers            7979008 bytes
Database mounted.
sys@ORCL>alter database archivelog;

Database altered.

sys@ORCL>alter database open;

Database altered.

sys@ORCL>archive log list;
Database log mode           Archive Mode
Automatic archival           Enabled
Archive destination           /u01/app/oracle/product/12.2.0/db_1/dbs/arch
Ol