Oracle 11g R2 Snapshot Standby

Oracle 11g introduces snapshot Standby, which allows Standby database to be opened in Read-write mode. When switching back to standby mode, all modifications in the Read-write mode are lost. It is implemented through the flashback database, but standby database does not need to explicitly enable flashback database.

If you use RAC, close all other instances and leave one instance. Make sure that the instance is in Mount mode.
Shutdown immediate;
startup Mount;

1. Close Managed Recovery
ALTER database RECOVER MANAGED STANDBY database CANCEL;

2. Convert standby to a snapshot standby.

SELECT flashback_on from V$database;

flashback_on
------------------
NO

ALTER DATABASE CONVERT to SNAPSHOT STANDBY;
ALTER DATABASE OPEN;
SELECT flashback_on from V$database;

flashback_on
------------------
RESTORE Point only

When you're done, you can treat standby like any Read-write database.

3. Convert standby back to physical standby, losing all modifications converted to snapshot standby.

SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ALTER DATABASE CONVERT to physical STANDBY;
SHUTDOWN IMMEDIATE;
STARTUP Nomount;
ALTER database MOUNT STANDBY DATABASE;
ALTER database RECOVER MANAGED STANDBY database DISCONNECT;
SELECT flashback_on from V$database;

flashback_on
------------------
NO

Now, standby back to managed recovery, and the transfer of archived logs resumed.
Note that the flashback database is still not open.

Oracle 11g R2 Snapshot Standby