Converting Between Physical Standby and Snapshot Standby Database (Oracle 12c)

First Few Basic Commands for Physical Standby Database

Start Redo Apply

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT;

OR

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING ARCHIVED LOGFILE DISCONNECT;

** Remember that in Oracle 12c, Real-time Redo Apply is enabled by Default. So, the first command will enable the real-time apply (This behavior is different than 11g version).
This means, if you have specified "DELAY" option in your Redo Transport parameter (log_archive_dest_n) on the primary database and you enable the redo apply using the first command on Standby Database in 12c version, then the database will ignore the DELAY option and apply the redo in real-time. (You will see a message similar to below in the alert.log file informing you that the DELAY option is ignored).

WARNING: Managed Standby Recovery started with REAL TIME APPLY
  DELAY 30 minutes specified at primary ignored

** If you want to use DELAY option in Oracle 12c, you must enable redo apply using the 2nd commnd.

Stop Redo Apply

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;


Monitor Redo Apply Progress

SQL> SELECT PROCESS, STATUS, THREAD#, SEQUENCE#, BLOCK#, BLOCKS FROM V$MANAGED_STANDBY;

Steps for converting Physical Standby Database into a Snapshot Standby Database 


1. Stop Redo Apply:
SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;

2. Ensure that the database is mounted:
SQL> SHITDOWN IMMEDIATE
SQL> STARTUP MOUNT
SQL> select name, open_mode, database_role from v$database;

3. Issue the following SQL command to perform the conversion
SQL> ALTER DATABASE CONVERT TO SNAPSHOT STANDBY;

4. Open the database in read/write mode
SQL> ALTER DATABASE OPEN READ WRITE;


Steps to Convert a Snapshot standby database into a Physical Standby Database

1. Stop the database and start in MOUNT mode
SQL> SHUTDOWN IMMEDIATE
SQL> STARTUP MOUNT

2. Issue the following SQL commands to perform the conversion
SQL> ALTER DATABASE CONVERT TO PHYSICAL STANDBY;

3. start Redo Apply
SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT;

OR

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING ARCHIVED LOGFILE DISCONNECT;

Few Things to Note :
* When the database is in the Snapshot Mode, the redo data will be received by the Standby database, but will not be applied.
* Redo data received while the database was a snapshot standby database is automatically applied when database is converted backto Physical Standby Mode and the Redo Apply is started.
* Snapshot standby database must be opened at least once in read-write mode before it can be converted into a physical standby database.


Steps to apply the redo until a given timestamp and then convert to Snapshot Standby

This steps can be used, if your standby database is running in Snapshot Standby Mode and you are planning to convert it back to Physical Standby, Apply the redo to a sepcific timestamp and then convert it back to Snapshot Standby mode and open the database in Read-Write Mode. (This is similar to do a fast forward your your Standby database to a given timestamp)

Assume that your Standby database is operating in Snapshot Standby Mode and is in Read-Write status.

1. Shutdown the database and start in Mount mode.
SQL> shutdown immediate
SQL> startup mount

2. Convert the database to Physical Standby Mode
SQL> ALTER DATABASE CONVERT TO PHYSICAL STANDBY;

3. Apply the Redo until the specified time
ALTER DATABASE RECOVER automatic standby database until time '2017-10-01 23:30:12';
** Follow the same timestamp format in your command.

4. Ensure that the database is mounted:
SQL> select name, open_mode, database_role from v$database;

3. Issue the following SQL command to perform the conversion
SQL> ALTER DATABASE CONVERT TO SNAPSHOT STANDBY;

4. Open the database in read/write mode
SQL> ALTER DATABASE OPEN READ WRITE;

The following step can be used, if your standby Database is in Physical Standby Mode and you are using DELAY option in your redo transport and you want to manually apply the log to a sepcific timestamp, which is not yet applied due to DELAY option. (Manually override the DELAY option).

Then open in Snapshot Standby Mode.

Assume that your Standby database is operating in Physical Standby Mode and Redo-Apply Mode is ON (With DELAY option)

1. Stop Redo Apply:

SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;

2. Apply the Redo until the specified time

ALTER DATABASE RECOVER automatic standby database until time '2017-10-01 23:30:12';

2. Ensure that the database is mounted:

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

3. Issue the following SQL command to perform the conversion

SQL> ALTER DATABASE CONVERT TO SNAPSHOT STANDBY;

4. Open the database in read/write mode

SQL> ALTER DATABASE OPEN READ WRITE;