Perform a switchover in a command-line tool

This topic describes how to switch the roles of the primary cluster and a standby cluster in a command-line tool.

You must first switch the primary cluster to the standby role and then switch the standby cluster to the primary role.

Preparations for a switchover

Before you perform a switchover, obtain the cluster information and select an appropriate standby cluster.

For more information, see Preparations for a switchover.

Switch the primary cluster to the standby role

Notice

Before you verify whether the primary cluster can be switched to the standby role, perform the following query operations on your OceanBase database.

1. 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
   

   Note:

   • The value of the SWITCHOVER_STATUS field 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 the value of the SWITCHOVER_STATUS field is TO STANDBY, the value of the SWITCHOVER_INFO field indicates the IDs of 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 are 2 and 3 can be switched to the primary role.

   • When the value of the SWITCHOVER_STATUS field is NOT ALLOWED, the value of the SWITCHOVER_INFO field indicates the reason why the switchover is not allowed. For example, CHECK PRIMARY CLUSTER SERVER STATUS indicates that the OBServer status of the primary cluster must be checked. To perform a primary/standby switchover, all OBServer nodes in the primary and standby OceanBase clusters must be active.

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

2. Execute the following statement 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
   

   The primary cluster is switched to the standby role, and the value of the SWITCHOVER_STATUS field changes to SWITCHOVER 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, execute the following statement 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 the value of the SWITCHOVER_STATUS field is TO PRIMARY, the standby cluster can be switched to the primary role. When the value of the SWITCHOVER_STATUS field is NOT ALLOWED, the standby cluster cannot be switched to the primary role. The value of the SWITCHOVER_INFO field indicates the reason.

   If no standby cluster can be switched to the primary role, you can execute the following statement 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. Execute the following statement 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
   

   The standby cluster is switched to the primary role. You can execute the following statement to query the V$OB_CLUSTER view and 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