ORACLE DG topic 5--switching between physical standby database and snapshot standby database

Preface

         Continuing the previous description, this article explains the last type of oracle DG standby database: snapshot—snapshot database. Unlike other standby databases, snapshot standby databases are fully updateable standby databases, switched from physical standby databases.

When the physical standby database is switched to the snapshot standby database, the snapshot continues to receive the redo log from the main database, but does not apply the redo log. At the same time, the snapshot is opened in read-write mode, allowing data to be read and written. The data written to the snapshot library will not be synchronized to the main library. When the subsequent switch back to the physical standby library, all the written data will be lost.

         The above snapshot feature can be used to temporarily open the read and write function in the test environment.

Related operations

Switch from physical backup to snapshot backup

• View the status of the physical standby database

SQL> select database_role,open_mode from v$database;   DATABASE_ROLE    OPEN_MODE ---------------- -------------------- PHYSICAL STANDBY READ ONLY WITH APPLY SYS >  select process,status from v$managed_standby;   PROCESS   STATUS --------- ------------ ARCH      CLOSING ARCH      CLOSING ARCH      CONNECTED ARCH      CLOSING RFS       IDLE RFS       IDLE RFS       IDLE RFS       IDLE MRP0      APPLYING_LOG   9 rows selected.

• Turn off real-time synchronization

SQL> recover managed standby database cancel;

• Switch to snapshot backup database

SQL> alter database convert to snapshot standby;

• Open the standby database

SQL> alter database open;

• View database role and open mode

SQL> select database_role,open_mode from v$database;

The entire process diagram is as follows:

      

Snapshot switch back to physical backup

• snapshot备库shutdown

SQL> shutdown immediate;

• Boot to mount state

SQL> startup mount;

• Switch to physical standby database

SQL> alter database convert to physical standby;

• Shutdown again

SQL> shutdown immediate;

• Boot to mount state

SQL> startup mount;

• The standby database starts the log application

SQL> recover managed standby database using current logfile disconnect

• View the status of the physical standby database

SQL> select database_role,open_mode from v$database;
SQL> select process,status from v$managed_standby;

The whole process is shown in the figure below: