The only requirement to have the snapshot standby is that FRA (Flash Recovery Area) must be configured on physical standby database. It is not necessary to have flashback enabled. Below are the steps on how to convert a physical standby database to a snapshot standby database and viceversa
SQL> startup mount
Oracle Database version: 11.2.0.3 Enterprise Edition
Primary database: DCPROC
Details with respect to the primary database:
SQL> select status,instance_name,database_role,open_mode from v$database,v$Instance;
STATUS INSTANCE_NAME DATABASE_ROLE OPEN_MODE
------------ ---------------- ---------------- --------------------
OPEN srprim PRIMARY READ WRITE
SQL> select thread#,max(sequence#) from v$archived_log group by thread#;
THREAD# MAX(SEQUENCE#)
------- --------------
1 206
Standby database Details:
Oracle database version: 11.2.0.3 Enterprise Edition
Standby database name: DRPROC
Details with respect to the physical standby database:
SQL> select status,instance_name,database_role,open_mode from v$database,v$Instance;
STATUS INSTANCE_NAME DATABASE_ROLE OPEN_MODE
------------ ---------------- ---------------- ----------------
OPEN DRPROC PHYSICAL STANDBY READ ONLY WITH APPLY
SQL> select thread#,max(sequence#) from v$archived_log where applied='YES' group by thread#;
THREAD# MAX(SEQUENCE#)
------- --------------
1 206
SQL> select flashback_on from v$database;
FLASHBACK_ON
------------------
NO
You can observe that the standby database is in sync with the primary database. Below outcome shows that the Flash Recovery Area is configured on the physical standby database.
SQL> show parameter db_recovery_file_dest
NAME TYPE VALUE
--------------------------- ----------- -------------
db_recovery_file_dest string +FRA_NEW
db_recovery_file_dest_size big integer 4122M
Step 1: Cancel the Managed Recovery Process (MRP) on the physical standby database, shut it down and place it in Mount mode.
SQL> alter database recover managed standby database cancel;
Database altered.
SQL> shut immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORA-32004: obsolete or deprecated parameter(s) specified for RDBMS instance
ORACLE instance started.
Total System Global Area 1269366784 bytes
Fixed Size 2227984 bytes
Variable Size 805306608 bytes
Database Buffers 452984832 bytes
Redo Buffers 8847360 bytes
Database mounted.
Step 2: Once the standby database is mounted, convert the Physical standby database to snapshot standby database.
SQL> alter database convert to snapshot standby;
Database altered.
Step 3: You can now open the snapshot standby database and check its mode.
SQL> alter database open;
Database altered.
SQL> select status,instance_name,database_role,open_mode from v$database,v$Instance;
STATUS INSTANCE_NAME DATABASE_ROLE OPEN_MODE
----------- --------------- ---------------- ------------------
OPEN DRPROC SNAPSHOT STANDBY READ WRITE
Small Test on the snapshot standby database.
1. Create a user called “SNAPTEST”
2. Create a table called “TEST” whose owner is “SNAPTEST” and insert some records in it. You can also update some of the records as well.
SQL> create user snaptest identified by oracle;
User created.
SQL> grant connect,resource to snaptest;
Grant succeeded.
SQL> conn snaptest/oracle@srps
Connected.
SQL> create table test(code number, name char(20));
Table created.
SQL> insert into test values (100,'ARUN');
1 row created.
SQL> insert into test values(200,'SHIVU');
1 row created.
SQL> commit;
Commit complete.
SQL> select * from test;
CODE NAME
---------- --------------------
100 ARUN
200 SHIVU
SQL> update snaptest.test set code=500 where name='ARUN';
1 row updated.
SQL> commit;
Commit complete.
SQL> select * from snaptest.test;
CODE NAME
---------- --------------------
500 ARUN
200 SHIVU
In the mean time, you can also see that the redo data from the primary database is received by the snapshot standby database but would not be applied.
On primary database the latest sequence generated is 208 and that on the standby database, the RFS process is idle for sequence 209.
Primary:
SQL> select thread#,max(sequence#) from v$archived_log group by thread#;
THREAD# MAX(SEQUENCE#)
---------- --------------
1 208
Standby:
SQL> select process,status,sequence# from v$managed_standby;
PROCESS STATUS SEQUENCE#
--------- ------------ ----------
ARCH CLOSING 1
ARCH CONNECTED 0
ARCH CONNECTED 0
ARCH CONNECTED 0
RFS IDLE 0
RFS IDLE 209
RFS IDLE 0
7 rows selected.
Steps on converting back a snapshot standby database to physical standby database.
Step 1: Shut down the snapshot standby database and open it in Mount mode.
SQL> shut immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORA-32004: obsolete or deprecated parameter(s) specified for RDBMS instance
ORACLE instance started.
Total System Global Area 1269366784 bytes
Fixed Size 2227984 bytes
Variable Size 805306608 bytes
Database Buffers 452984832 bytes
Redo Buffers 8847360 bytes
Database mounted.
Step 2: Convert the snapshot standby database to physical standby database.
SQL> alter database convert to physical standby;
Database altered.
Step 3: Once done, bounce the physical standby database and start the Managed Recovery Process (MRP) on it.
SQL> shut immediate
ORA-01507: database not mounted
ORACLE instance shut down.
SQL> startup
ORA-32004: obsolete or deprecated parameter(s) specified for RDBMS instance
ORACLE instance started.
Total System Global Area 1269366784 bytes
Fixed Size 2227984 bytes
Variable Size 805306608 bytes
Database Buffers 452984832 bytes
Redo Buffers 8847360 bytes
Database mounted.
Database opened.
SQL> select status,instance_name,database_role,open_mode from v$database,v$Instance;
STATUS INSTANCE_NAME DATABASE_ROLE OPEN_MODE
------------ -------------- ---------------- ----------------
OPEN DRPROC PHYSICAL STANDBY READ ONLY
SQL> alter database recover managed standby database disconnectfrom session;
Database altered.
SQL> select process,status,sequence# from v$managed_standby;
PROCESS STATUS SEQUENCE#
--------- ------------ ----------
ARCH CONNECTED 0
ARCH CONNECTED 0
ARCH CONNECTED 0
ARCH CONNECTED 0
RFS IDLE 0
RFS IDLE 0
RFS IDLE 0
MRP0 WAIT_FOR_LOG 213
8 rows selected.
Crosscheck whether the physical standby database is in sync with the primary database.
On Primary database:
SQL> select thread#,max(sequence#) from v$archived_log group bythread#;
THREAD# MAX(SEQUENCE#)
---------- --------------
1 212
On Standby database:
SQL> select thread#,max(sequence#) from v$archived_log where applied='YES' group by thread#;
THREAD# MAX(SEQUENCE#)
---------- --------------
1 212
You can see below that the transactions that were carried out when the standby database is opened in READ WRITE mode are flushed out after it was converted back to physical standby database mode.
SQL> select * from snaptest.test;
select * from snaptest.test
*
ERROR at line 1:
ORA-00942: table or view does not exist
SQL> select username,account_status from dba_users where username='SNAPTEST';
no rows selected
