Snapshot standby模式

    客户某生产业务增量生产时发现数据库会切换Snapshot standby模式。进行学习测试。

一、原理说明

在Oracle 11g中,data guard最吸引人的active data guard的实时查询特性(即可以以只读方式打开物理standby数据库的同时MRP进程能继续做recover),快照备用数据库这个特性也是不错,比较适用于快速部署一个临时的与线上环境相同的测试数据库.它是通过还原点(restore point)和闪回数据库的原理(flashback database),可以以读/写方式打开物理备用数据库,对数据库进行修改,之后再根据还原点,恢复到物理备用数据库。

Snapshot standby模式，即在备库进行，开启此模式时为了在备库进行一些测试操作，而又不行留存在数据库中，当备库切换回physical standby物理备库时，之前在snapshot standby模式进行的测试将会被丢弃

备注:

物理standby是最高保护模式(maximum protection),是不能转换为snapshot standby的.

物理standby使用了standby redo log,在create restore point后,要alter system switch logfile;,以保证还原点的scn在物理standby库上是归档的,不然可能无法成功闪回到还原点.

物理standby在切换为快照standby后,如果间隔很长时间,primary数据库产生的大量的重做日志,这样可以在转换为物理standby后,通过对primary数据库的增量备份并recover到物理standby,来加快物理standby的还原速度.

注意：

1.需首先确认备库已经结束日志应用了！（本次测试因为没有确认导致部分步骤报错）

2.snapshot standby模式时，闪回数据库功能可开启也也可关闭，默认是关闭状态；但必须设置快速恢复区大小及路径

二、备库节点node2测试步骤：

[oracle@node2 ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.4.0 Production on Tue Jun 19 21:46:34 2018

Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to:

Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> select * from v$version;

BANNER

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

Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

PL/SQL Release 11.2.0.4.0 - Production

CORE    11.2.0.4.0      Production

TNS for Linux: Version 11.2.0.4.0 - Production

NLSRTL Version 11.2.0.4.0 - Production

SQL> select flashback_on from v$database;

FLASHBACK_ON

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

NO

SQL> select open_mode,database_role from v$database;

OPEN_MODE            DATABASE_ROLE

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

READ ONLY WITH APPLY PHYSICAL STANDBY

SQL> select status from v$instance;

STATUS

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

OPEN

SQL> alter database convert to snapshot standby;

alter database convert to snapshot standby

*

ERROR at line 1:

ORA-38784: Cannot create restore point 'SNAPSHOT_STANDBY_REQUIRED_06/15/2018

02:27:25'.

ORA-01153: an incompatible media recovery is active

查询网络资料：

ORA-01153: an incompatible media recovery is active

Cause: Attempted to start an incompatible media recovery or open resetlogs

during media recovery or RMAN backup . Media recovery sessions are

incompatible if they attempt to recover the same data file. Incomplete media

recovery or open resetlogs is incompatible with any media recovery. Backup or

restore by RMAN is incompatible with open resetlogs

Action: Complete or cancel the other media recovery session or RMAN backup

解决方法：

SQL> alter database recover managed standby database cancel;

Database altered.

SQL> alter database  recover managed standby database using current logfile disconnect from session; 

Database altered.

SQL> select open_mode,database_role from v$database;

OPEN_MODE            DATABASE_ROLE

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

MOUNTED              PHYSICAL STANDBY

SQL> alter database open;

alter database open

*

ERROR at line 1:

ORA-10456: cannot open standby database; media recovery session may be in progress

原因：开启备库应用日志之后没取消应用日志，直接启库，报错

SQL> alter database recover managed standby database cancel;

Database altered.

SQL> alter database open;

Database altered.

SQL> select open_mode,database_role from v$database;

OPEN_MODE            DATABASE_ROLE

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

READ ONLY            PHYSICAL STANDBY

SQL> alter database convert to snapshot standby;

alter database convert to snapshot standby

*

ERROR at line 1:

ORA-38784: Cannot create restore point 'SNAPSHOT_STANDBY_REQUIRED_06/15/2018

02:46:02'.

ORA-38786: Recovery area is not enabled.

创建一个目录用于存放快速恢复区

[root@node2 oradata]# su - oracle

[oracle@node2 ~]$ cd /oradata/

[oracle@node2 oradata]$ mkdir recovery

SQL> show parameter recovery;

NAME                                 TYPE        VALUE

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

db_recovery_file_dest                string

db_recovery_file_dest_size           big integer 4182M

recovery_parallelism                 integer     0

SQL> alter system set db_recovery_file_dest='/oradata/recovery';

System altered.

SQL> alter system set db_recovery_file_dest_size=2G;

System altered.

解决完报错就可以执行快照

SQL> alter database convert to snapshot standby;

Database altered.

三、查看快照信息（可以查看alert日志，会发现数据库创建了一个guaranteed restore point,确保我们切回主备，可应用日志)

[oracle@node2 trace]$ tail -f alert_orcls.log 

alter database convert to snapshot standby

Starting background process RVWR

Fri Jun 15 02:51:28 2018

RVWR started with pid=19, OS id=7250 

Allocated 3981120 bytes in shared pool for flashback generation buffer

Created guaranteed restore point SNAPSHOT_STANDBY_REQUIRED_06/15/2018 02:51:28

Killing 3 processes with pids 7193,7197,7195 (all RFS) in order to disallow current and future RFS connections. Requested by OS process 7182

All dispatchers and shared servers shutdown

CLOSE: killing server sessions.

CLOSE: all sessions shutdown successfully.

四、查看备库数据库状态，进行测试

SQL>select open_mode,database_role from v$database;

OPEN_MODE            DATABASE_ROLE

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

MOUNTED              SNAPSHOT STANDBY

SQL>  select flashback_on from v$database;

FLASHBACK_ON

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

RESTORE POINT ONLY

SQL>  select open_mode,database_role from v$database;

OPEN_MODE            DATABASE_ROLE

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

MOUNTED              SNAPSHOT STANDBY

SQL> alter database open;

Database altered.

SQL> select open_mode,database_role from v$database;

OPEN_MODE            DATABASE_ROLE

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

READ WRITE           SNAPSHOT STANDBY

做测试

SQL> CREATE TABLE ZHU (A INT);

Table created.

SQL> INSERT INTO ZHU VALUES (1);

1 row created.

SQL> COMMIT;

Commit complete.

SQL> SELECT * FROM ZHU;

         A

----------

         1

五、 恢复物理备库，数据库需要在mount下完成切换 ，并验证测试         

SQL> shutdown immediate;

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL> startup mount;

ORACLE instance started.

Total System Global Area  776646656 bytes

Fixed Size                  2257272 bytes

Variable Size             507514504 bytes

Database Buffers          264241152 bytes

Redo Buffers                2633728 bytes

Database mounted.

SQL> alter database convert to physical standby;

Database altered.

SQL> select status from v$instance;

STATUS

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

STARTED

切换完成后需要重启到mount应用日志         

SQL> shutdown immediate;

ORA-01507: database not mounted

ORACLE instance shut down.

SQL> startup mount;

ORACLE instance started.

Total System Global Area  776646656 bytes

Fixed Size                  2257272 bytes

Variable Size             507514504 bytes

Database Buffers          264241152 bytes

Redo Buffers                2633728 bytes

Database mounted.

SQL> alter database recover managed standby database using current logfile disconnect from session; 

Database altered.

SQL> alter database recover managed standby database cancel;

Database altered.

SQL> select database_role,open_mode from v$database;

DATABASE_ROLE    OPEN_MODE

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

PHYSICAL STANDBY MOUNTED

SQL>  alter database open; 

Database altered.

SQL>  select database_role,open_mode from v$database;

DATABASE_ROLE    OPEN_MODE

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

PHYSICAL STANDBY READ ONLY

验证在SNAPSHOT STANDBY模式下创建的表

SQL> select * from ZHU;

select * from ZHU

              *

ERROR at line 1:

ORA-00942: table or view does not exist