ORACLE 11g PHYSICAL STANDBY已经不仅仅只提供灾难恢复功能，其ACTI VE DATA GUARD 特性让备库处于

RED ONLY状态，可以提供做报表查询、读写分离使用；还新增了SNAPSHOT STANDBY 特性，此特性能让备库

暂时处于可读可写状态，为各种性能、压力测试提供了环境，重要的是测试完成后又可转换回PHYSICAL STANDBY，

备库的数据继续与主库保持一致。

SNAPSHOT STANDBY 限制及条件

1. 只有PHYSICAL STANDBY能转换为SNAPSHOT STANDBY。

2. DB_RECOVERY_FILE_DEST必需设置，这里FLASHBACK DATABASE不是必须的。

3.只有PHYSICAL STANDBY 处于mount模式才能转换为SNAPSHOT STANDBY。

设置闪回恢复区

SQL> alter system set DB_RECOVERY_FILE_DEST_SIZE=500m scope=both;

System altered.

SQL> alter system set db_recovery_file_dest='/u01/arch/flasharch' scope=both;

System altered.

SQL> select FLASHBACK_ON from v$database;

FLASHBACK_ON
------------------
NO

查看备库目前模式

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

DATABASE_ROLE     DB_UNIQUE_NAME         OPEN_MODE
---------------- ------------------------------ --------------------
PHYSICAL STANDBY ogg                READ ONLY WITH APPLY

此时备库为PHYSICAL STANDBY，正处于READ ONLY REAL TIME APPLY 模式

取消备库恢复管理模式

SQL> alter database recover managed standby database cancel;

Database altered.

创建SNAPSHOT STANDBY

创建SNAPSHOT STANDBY 命令非常简单

SQL> alter database convert to snapshot standby;

Database altered.

查看alter log 里面的信息，命令已经执行完成，ORACLE创建了guaranteed restore point

Managed Standby Recovery Canceled (ogg)
Completed: alter database recover managed standby database cancel
Wed Oct 30 11:08:18 2013
alter database convert to snapshot standby
Starting background process RVWR
Wed Oct 30 11:08:18 2013
RVWR started with pid=26, OS id=5156
Allocated 3981204 bytes in shared pool for flashback generation buffer
Created guaranteed restore point SNAPSHOT_STANDBY_REQUIRED_10/30/2013 11:08:18

查看备库模式已经变为SNAPSHOT STADNBY
SQL>  select database_role,db_unique_name,open_mode from v$database;

DATABASE_ROLE     DB_UNIQUE_NAME         OPEN_MODE
---------------- ------------------------------ --------------------
SNAPSHOT STANDBY ogg                MOUNTED

查看闪回恢复区已经产生文件
SQL> !ls -lt /u01/arch/flasharch/OGG/flashback
total 102528
-rw-r----- 1 oracle oinstall 52436992 Oct 30 11:37 o1_mf_970y12xh_.flb
-rw-r----- 1 oracle oinstall 52436992 Oct 30 11:08 o1_mf_970y15og_.flb

开启备库，进行写测试

SQL> alter database open;

Database altered.

在备库创建一个新用户

SQL> create user xhl_snapstb identified by xhl;

User created.

SQL> grant dba to xhl_snapstb;

Grant succeeded.

在备库创建一个新表

SQL> create table xhl_snapstb.xhl as select * from dba_users;

Table created.

SQL> select count(*) from xhl_snapstb.xhl;

  COUNT(*)
----------
     9

删除原有表

SQL> select table_name,TABLESPACE_NAME from dba_tables where tablespace_name = 'TBS_XHL';

TABLE_NAME               TABLESPACE_NAME
------------------------------ ------------------------------
XHL                   TBS_XHL

SQL> DROP TABLE XHL PURGE;

Table dropped.

DROP TABLESPACE测试

Wed Oct 30 11:23:47 2013
drop tablespace TBS_XHL  including c