Switchover

When the primary tenant is available, you can switch the roles of the primary tenant and a standby tenant without data loss.

Background

A switchover is completed in the following three steps: preparing for the switchover, switching the primary tenant to the STANDBY role, and switching a standby tenant to the PRIMARY role.

The following figure shows the switchover process.

Prepare for the switchover

Before you switch a standby tenant to the PRIMARY role, you must specify the log archiving destination and enable archivelog for the standby tenant. To ensure data consistency between the primary and standby tenants, which is required for a successful switchover, you must also set the synchronization mode of the standby tenant to continuous synchronization.

1. Log on to the database as the administrator of the standby tenant or the sys tenant of the cluster where the standby tenant resides.

2. Specify the log archiving destination of the standby tenant.

   To do so, specify the following attributes: LOCATION, PIECE_SWITCH_INTERVAL, and BINDING.

   • Execute the following statement in the sys tenant of the cluster where the standby tenant resides to specify the log archiving destination of the standby tenant:

     ALTER SYSTEM SET LOG_ARCHIVE_DEST='LOCATION = archive_path [PIECE_SWITCH_INTERVAL = piece_switch_interval] [BINDING = archive_mode]' TENANT = tenant_name;
     

   • Execute the following statement in the standby tenant to specify the log archiving destination of the current tenant:

     ALTER SYSTEM SET LOG_ARCHIVE_DEST='LOCATION = archive_path [PIECE_SWITCH_INTERVAL = piece_switch_interval] [BINDING = archive_mode]';
     

   Attributes:

   • The LOCATION attribute specifies the archiving destination. OceanBase Database supports two types of media as the archiving destination: Network File System (NFS) and Alibaba Cloud Object Storage Service (OSS).

   • The BINDING attribute specifies the prioritizing mode for archiving and businesses. The BINDING attribute has two values: Optional and Mandatory. If you do not specify this attribute, the default value Optional takes effect.

     • The Optional mode prioritizes user businesses. In this mode, when log archiving falls behind log generation, logs may be recycled before being archived. This causes interruption.

     • The Mandatory mode prioritizes archiving. In this mode, you may be unable to write more data before existing data is archived.

   • The PIECE_SWITCH_INTERVAL attribute specifies the switching interval for pieces. The value range is [1d, 7d]. If you do not specify this attribute, the default value 1d takes effect.

   For example, to set NFS as the archiving destination, execute the following statement to set the log archiving path of the standby tenant to file:///data/1/nfs/backup//ob_oracle_standby/archive and set BINDING to Optional:

   obclient [ORACLE]> ALTER SYSTEM SET LOG_ARCHIVE_DEST='LOCATION = file:///data/1/nfs/backup//ob_oracle_standby/archive BINDING = optional' TENANT = oracle_standby;
   
   obclient [ORACLE]> ALTER SYSTEM SET LOG_ARCHIVE_DEST='LOCATION = file:///data/1/nfs/backup//ob_oracle_standby/archive BINDING = optional';
   

3. Enable archivelog for the standby tenant.

   • Execute the following statement in the sys tenant of the cluster where the standby tenant resides to enable archivelog for the standby tenant.

     Sample statement:

     obclient [(none)]> ALTER SYSTEM ARCHIVELOG TENANT = oracle_standby;
     

     oracle_standby indicates the name of the standby tenant. Replace it with the actual name of your standby tenant.

   • Execute the following statement in the standby tenant to enable archivelog for the current tenant.

     obclient [xx]> ALTER SYSTEM ARCHIVELOG;
     

4. Check whether the standby tenant is in continuous synchronization mode.

   You can query the DBA_OB_TENANTS view and check the value of the RECOVERY_UNTIL_SCN column. The value of the RECOVERY_UNTIL_SCN column indicates the maximum recovery system change number (SCN).

   Sample statement:

   SELECT TENANT_NAME, TENANT_ROLE, SWITCHOVER_STATUS, RECOVERY_UNTIL_SCN
   FROM oceanbase.DBA_OB_TENANTS WHERE TENANT_NAME = 'oracle_standby';
   +------------------+-------------+-------------------+------------------------+
   | TENANT_NAME      | TENANT_ROLE | SWITCHOVER_STATUS | RECOVERY_UNTIL_SCN     |
   +------------------+-------------+-------------------+------------------------+
   | oracle_standby   | STANDBY     | NORMAL            | 4611686018427387903    |
   +------------------+-------------+-------------------+------------------------+
   1 row in set
   

   In the query result, if the value of the RECOVERY_UNTIL_SCN column is equal to the value of the maximum SCN, which is 4611686018427387903, the standby tenant is in continuous log synchronization mode.

   For more information about the DBA_OB_TENANTS view, see oceanbase.DBA_OB_TENANTS (MySQL Mode) or DBA_OB_TENANTS (Oracle Mode).

5. (Optional) If the standby tenant is not in continuous log synchronization mode, execute the following statement:

   ALTER SYSTEM RECOVER STANDBY UNTIL UNLIMITED;
   

   To execute the statement in the sys tenant, you must use the TENANT = tenant_name parameter to specify the name of the standby tenant in the statement, for example, ALTER SYSTEM RECOVER STANDBY TENANT = oracle_standby UNTIL UNLIMITED;.

   After the standby tenant enters the continuous log synchronization mode, wait for the standby tenant to synchronize logs from the primary tenant. For more information about how to view the log synchronization progress of a standby tenant, see Monitor the log synchronization status of a standby tenant.

Switchover

The switchover step includes switching the primary tenant to the STANDBY role and switching a standby tenant to the PRIMARY role.

1. Switch the primary tenant to the STANDBY role.

   1. Log on to the database as the administrator of the primary tenant or the sys tenant of the cluster where the primary tenant resides.

   2. Execute the SWITCHOVER statement to switch the primary tenant to the STANDBY role.

      • Execute the following statement in the sys tenant of the cluster where the primary tenant resides to switch the primary tenant to the STANDBY role:

        ALTER SYSTEM SWITCHOVER TO STANDBY TENANT = tenant_name;
        

      • Execute the following statement in the primary tenant to switch it to the STANDBY role:

        ALTER SYSTEM SWITCHOVER TO STANDBY;
        

   3. Check whether the primary tenant is switched to the STANDBY role.

      Sample statement:

      SELECT TENANT_ID, TENANT_NAME,TENANT_TYPE,TENANT_ROLE,SWITCHOVER_STATUS
      FROM DBA_OB_TENANTS
      WHERE TENANT_NAME='oracle';
      +-----------+-------------+-------------+-------------+-------------------+
      | TENANT_ID | TENANT_NAME | TENANT_TYPE | TENANT_ROLE | SWITCHOVER_STATUS |
      +-----------+-------------+-------------+-------------+-------------------+
      |      1004 | oracle      | USER        | STANDBY     | NORMAL            |
      +-----------+-------------+-------------+-------------+-------------------+
      1 row in set
      

      The query result shows that the value of the TENANT_ROLE parameter of the original primary tenant has changed to STANDBY. If the value of the SWITCHOVER_STATUS parameter is NORMAL, the original primary tenant is switched to the STANDBY role.

   4. Query the V$OB_ARCHIVE_DEST_STATUS view and check the SYNCHRONIZED column to verify whether the log archiving of the original primary tenant is completed.

      Sample statement:

      SELECT * FROM V$OB_ARCHIVE_DEST_STATUS WHERE TENANT_ID = 1004;
      

      If the value of the SYNCHRONIZED field in the query result is YES, the log archiving of the original primary tenant is completed.

2. Switch a standby tenant to the PRIMARY role.

   1. Log on to the database as the administrator of the standby tenant or the sys tenant of the cluster where the standby tenant resides.

   2. Execute the SWITCHOVER statement to switch the standby tenant to the PRIMARY role.

      Notice

      Before the SWITCHOVER statement is executed, the system checks whether all logs are synchronized from the recovery source to the standby tenant. Therefore, the execution time of the SWITCHOVER statement depends on the progress of the progress of synchronization between the standby tenant and the original primary tenant.

      • Execute the following statement in the sys tenant of the cluster where the standby tenant resides to switch the standby tenant to the PRIMARY role:

        ALTER SYSTEM SWITCHOVER TO PRIMARY TENANT = tenant_name;
        

      • Execute the following statement in the standby tenant to switch it to the PRIMARY role:

        ALTER SYSTEM SWITCHOVER TO PRIMARY;
        

   3. Check whether the standby tenant is switched to the PRIMARY role.

      Sample statement:

      SELECT TENANT_ID, TENANT_NAME,TENANT_TYPE,TENANT_ROLE,SWITCHOVER_STATUS
      FROM DBA_OB_TENANTS
      WHERE TENANT_NAME='oracle_standby';
      +-----------+----------------------------+-------------+-------------+-------------------+
      | TENANT_ID | TENANT_NAME                | TENANT_TYPE | TENANT_ROLE | SWITCHOVER_STATUS |
      +-----------+----------------------------+-------------+-------------+-------------------+
      |      1006 | oracle_standby             | USER        | PRIMARY     | NORMAL            |
      +-----------+----------------------------+-------------+-------------+-------------------+
      1 row in set
      

      The query result shows that the value of the TENANT_ROLE parameter of the original standby tenant has changed to PRIMARY. If the value of the SWITCHOVER_STATUS parameter is NORMAL, the standby tenant is switched to the PRIMARY role.

      For more information about the DBA_OB_TENANTS view, see oceanbase.DBA_OB_TENANTS (MySQL Mode) or DBA_OB_TENANTS (Oracle Mode).

3. Specify the recovery source of the new standby tenant, namely the original primary tenant, to receive archive logs from the new primary tenant.

   1. Log on to the database as the administrator of the new standby tenant or the sys tenant of the cluster where the new standby tenant resides.

   2. Execute the following statement to specify the recovery source of the new standby tenant.

      • Execute the following statement in the sys tenant of the cluster where the new standby tenant resides to specify the recovery source of the new standby tenant:

        ALTER SYSTEM SET LOG_RESTORE_SOURCE ='LOCATION = archive_path' TENANT = tenant_name;
        

      • Execute the following statement in the new standby tenant to specify its recovery source:

        ALTER SYSTEM SET LOG_RESTORE_SOURCE ='LOCATION = archive_path';
        

      The LOCATION attribute specifies the log archiving destination of the new primary tenant.

      Sample statement:

      obclient [SYS]> ALTER SYSTEM SET LOG_RESTORE_SOURCE ='LOCATION = file:///data/1/nfs/backup//ob_oracle_standby/archive' TENANT = oracle;
      
      obclient [SYS]> ALTER SYSTEM SET LOG_RESTORE_SOURCE ='LOCATION = file:///data/1/nfs/backup//ob_oracle_standby/archive';
      

   After you specify the recovery source, you do not need to execute the RECOVER statement to set the recovery endpoint of the original primary tenant. This is because the recovery endpoint of the original primary tenant is set to UNLIMITED by default.