Switchover by using commands

This topic describes how to switch the roles of the primary cluster and a standby cluster by using commands.

Switch the primary cluster to the standby role

1. Verify that the primary cluster can be switched to the standby role.

   Query the SWITCHOVER_STATUS and SWITCHOVER_INFO fields in the V$OB_CLUSTER view of the primary cluster.

   Example:

   obclient> SELECT SWITCHOVER_STATUS, SWITCHOVER_INFO FROM V$OB_CLUSTER;
   +-------------------+------------------------------+
   | SWITCHOVER_STATUS |          SWITCHOVER_INFO              |
   +-------------------+------------------------------+
   |         TO STANDBY        | SYNCED STANDBY CLUSTERS: 2,3 |
   +-------------------+------------------------------+
   1 row in set
   

   In the example:

   • SWITCHOVER_STATUS indicates the current switchover status. TO STANDBY indicates that the primary cluster can be switched to the standby role. NOT ALLOWED or another value indicates that the switchover condition is not met.

   • When SWITCHOVER_STATUS is TO STANDBY, SWITCHOVER_INFO indicates the candidate standby clusters that can be switched to the primary role. For example, SYNCED STANDBY CLUSTERS: 2,3 indicates that the standby clusters whose cluster IDs (CLUSTER_ID) are respectively 2 and 3 can be switched to the primary role.

   • When SWITCHOVER_STATUS is NOT ALLOWED, SWITCHOVER_INFO indicates the reason why switchover is not allowed. For example, CHECK PRIMARY CLUSTER SERVER STATUS indicates that the server status of the primary cluster must be checked. OceanBase Database requires that all servers be active during switchover. If some servers are inactive, switchover is not allowed.

     For information about troubleshooting methods corresponding to the values of the SWITCHOVER_INFO field, see Switchover errors.

2. Run the following command on the primary cluster to switch its role to PHYSICAL STANDBY:

   obclient>  ALTER SYSTEM COMMIT TO SWITCHOVER TO PHYSICAL STANDBY;
   Query OK, 0 rows affected
   

   After the command is executed, the primary cluster is switched to the standby role, and SWITCHOVER_STATUS changes to SWTICHOVER SWITCHING.

   obclient> SELECT CLUSTER_ID, CLUSTER_ROLE, SWITCHOVER_STATUS FROM V$OB_CLUSTER;
   +------------+------------------+----------------------+
   | CLUSTER_ID |    CLUSTER_ROLE     |    SWITCHOVER_STATUS    |
   +------------+------------------+----------------------+
   |                  1 | PHYSICAL STANDBY | SWITCHOVER SWITCHING |
   +------------+------------------+----------------------+
   1 row in set
   

Switch a standby cluster to the primary role

1. In the target standby cluster, run the following command to verify that it can be switched to the primary role:

   obclient> SELECT SWITCHOVER_STATUS, SWITCHOVER_INFO FROM V$OB_CLUSTER;
   +-------------------+-----------------+
   | SWITCHOVER_STATUS | SWITCHOVER_INFO |
   +-------------------+-----------------+
   | TO PRIMARY        |                 |
   +-------------------+-----------------+
   1 row in set
   

   When SWITCHOVER_STATUS is TO PRIMARY, the standby cluster can be switched to the primary role. When SWITCHOVER_STATUS is NOT ALLOWED, the standby cluster cannot be switched to the primary role, and SWITCHOVER_INFO indicates the reason.

   If no standby cluster can be switched to the primary role, you can run the following command on the original primary cluster to switch it back to the primary role:

   obclient> ALTER SYSTEM COMMIT TO SWITCHOVER TO PRIMARY;                                                                                                                                                           
   Query OK, 0 rows affected
   

2. Run the following command on the target standby cluster to switch it to the primary role:

   obclient> ALTER SYSTEM COMMIT TO SWITCHOVER TO PRIMARY;                                                                                                                                                           
   Query OK, 0 rows affected
   

   After the command is executed, the standby cluster is switched to the primary role. You can run the following command to query the V$OB_CLUSTER view to verify the switching result:

   obclient> SELECT CLUSTER_ID, CLUSTER_ROLE, SWITCHOVER_STATUS, SWITCHOVER_INFO FROM V$OB_CLUSTER;
   +------------+--------------+-------------------+------------------------------+
   | CLUSTER_ID | CLUSTER_ROLE | SWITCHOVER_STATUS |          SWITCHOVER_INFO              |
   +------------+--------------+-------------------+------------------------------+
   |                   2 |     PRIMARY      |         TO STANDBY        | SYNCED STANDBY CLUSTERS: 1,3 |
   +------------+--------------+-------------------+------------------------------+
   1    row in set