【12c】数据库闪回与Data Guard

在Data Guard环境中可以利用数据库的闪回特性将备库以读写模式打开，用于执行对主数据库的某种测试工作，当测试完毕后，再将数据库闪回到之前的状态，作为备份继续提供保护服务。

1 在备库闪回数据库

1）取消备库托管恢复

SQL> alter database recover managed standby database cancel;



Database altered.

2）设置备库的闪回恢复区

SQL> show parameter db_recover



NAME TYPE VALUE

------------------------------------ ----------- ------------------------------

db_recovery_file_dest string /u01/app/oracle/fast_recovery_

area

db_recovery_file_dest_size big integer 4560M

3）启动闪回特性

SQL> startup mount

ORACLE instance started.



Total System Global Area 1644167168 bytes

Fixed Size 2925024 bytes

Variable Size 1073745440 bytes

Database Buffers 553648128 bytes

Redo Buffers 13848576 bytes

Database mounted.

SQL> alter database flashback on;



Database altered.



SQL> select flashback_on from v$database;



FLASHBACK_ON

------------------

YES

4）创建一个保证还原点

SQL> create restore point before_opem_rw guarantee flashback database;



Restore point created.

5）将主库向备库传输日志的目标目的地设置为延迟状态

SQL> show parameter log_archive_dest_2



NAME TYPE VALUE

------------------------------------ ----------- ------------------------------

log_archive_dest_2 string SERVICE=shhai LGWR ASYNC

VALID_FOR=(ONLINE_LOGFILES,P

RIMARY_ROLE)

DB_UNIQUE_NAME=orcldg

SQL> show parameter log_archive_dest_state_2



NAME TYPE VALUE

------------------------------------ ----------- ------------------------------

log_archive_dest_state_2 string ENABLE

SQL> alter system set log_archive_dest_state_2='defer';



System altered.

6）激活物理备库，将备库转换为独立的数据库运行

SQL> alter database activate physical standby database;



Database altered.

SQL> alter database open;



Database altered.



SQL> select database_role,open_mode,flashback_on from v$database;



DATABASE_ROLE OPEN_MODE FLASHBACK_ON

---------------- -------------------- ------------------

PRIMARY READ WRITE YES

7）在激活后的备库执行测试等各种操作

8）测试完毕，将数据库闪回到保证还原点

SQL> shutdown abort

ORACLE instance shut down.

SQL> startup mount

ORACLE instance started.



Total System Global Area 1644167168 bytes

Fixed Size 2925024 bytes

Variable Size 1073745440 bytes

Database Buffers 553648128 bytes

Redo Buffers 13848576 bytes

Database mounted.

SQL> flashback database to restore point before_opem_rw;



Flashback complete.

SQL> select database_role,open_mode,flashback_on from v$database;



DATABASE_ROLE OPEN_MODE FLASHBACK_ON

---------------- -------------------- ------------------

PRIMARY MOUNTED YES

此时，数据库仍然使独立的数据库，只是状态回到了还原点。

9）将数据库转换为备库

SQL> alter database convert to physical standby ;



Database altered.



SQL> select database_role,open_mode,flashback_on from v$database;



DATABASE_ROLE OPEN_MODE FLASHBACK_ON

---------------- -------------------- ------------------

PHYSICAL STANDBY MOUNTED YES



SQL> alter database open;



Database altered.

10）在主库启用向备库的日志传输

SQL> alter system set log_archive_dest_state_2='enable';



System altered.

11）启动物理备库的日志应用

SQL> alter database recover managed standby database disconnect from session;



Database altered.



SQL> select database_role,open_mode,flashback_on from v$database;



DATABASE_ROLE OPEN_MODE FLASHBACK_ON

---------------- -------------------- ------------------

PHYSICAL STANDBY READ ONLY WITH APPLY YES

上述演示展示了创建还原点将备库激活，以读写模式打开，进行一系列的测试，并利用闪回技术还原，之后再将其转为备库，整个过程比较繁琐，并且再备库以读写模式打开后，实际上是作为一个独立的数据库存在，但这个期间数据库停止接收了来自主库的重做日志，这在一定程度上就失去了对主库的保护，那么有没有一种方法，在使备库处于读写状态时，可以继续接收重做日志，只是不应用？

快照数据库（Snapshot standby database）可以做到，下面将进行演示。

2 快照备用数据库

1）取消备库托管恢复

SQL> alter database recover managed standby database cancel;



Database altered.

2）将备库转换为快照数据库

SQL> alter database convert to snapshot standby;



Database altered.

SQL> select database_role,open_mode,flashback_on from v$database;



DATABASE_ROLE OPEN_MODE FLASHBACK_ON

---------------- -------------------- ------------------

SNAPSHOT STANDBY MOUNTED YES

3）打开数据库

SQL> alter database open;



Database altered.



SQL> select database_role,open_mode,flashback_on from v$database;



DATABASE_ROLE OPEN_MODE FLASHBACK_ON

---------------- -------------------- ------------------

SNAPSHOT STANDBY READ WRITE YES

4）在快照数据库执行一系列的测试等操作；

5）转换快照数据库为物理备库

SQL> shutdown abort

ORACLE instance shut down.

SQL> startup mount

ORACLE instance started.



Total System Global Area 1644167168 bytes

Fixed Size 2925024 bytes

Variable Size 1073745440 bytes

Database Buffers 553648128 bytes

Redo Buffers 13848576 bytes

Database mounted.

SQL> alter database convert to physical standby;



Database altered.



SQL> alter database open;



Database altered.

6）备库开启托管恢复

SQL> alter database recover managed standby database disconnect from session;



Database altered.

7）主库修改数据

SQL> update scott.emp set comm=1000 where empno=7369;



1 row updated.



SQL> commit;



Commit complete.



SQL> select * from scott.emp where empno=7369;



EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

---------- ---------- --------- ---------- --------- ---------- ---------- ----------

7369 SMITH CLERK 7902 17-DEC-80 800 1000 20

8）备库验证，一致。

SQL> select * from scott.emp where empno=7369;



EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

---------- ---------- --------- ---------- --------- ---------- ---------- ----------

7369 SMITH CLERK 7902 17-DEC-80 800 1000 20