Cancel a replica task

One log stream of a tenant supports only one replica task at a time. You can perform a new task only after the ongoing task is completed. If you want to perform an emergency task with priority, you can execute the ALTER SYSTEM CANCEL REPLICA TASK statement to cancel the ongoing replica task and then initiate the emergency task.

Limitations

• You can cancel only a replica adding or migration task.

• You can cancel replica tasks of all tenants in the sys tenant but cancel only replica tasks of the current tenant in a user tenant.

Prerequisites

• You have the ALTER SYSTEM privilege.

• You have the SELECT privilege on the following views:

  • DBA_OB_LS_REPLICA_TASKS and CDB_OB_LS_REPLICA_TASKS

  • DBA_OB_LS_REPLICA_TASK_HISTORY and CDB_OB_LS_REPLICA_TASK_HISTORY

Procedure

Assume that a task to migrate a read-only replica of log stream 1001 of a tenant named tenant1 is in progress and a full-featured replica needs to be added to an available OBServer node to ensure high availability upon an exception of the cluster. However, the read-only replica involves a large amount of data, and the replica migration task is unlikely to complete anytime soon. Consequently, the emergency task to add a full-featured replica cannot be performed immediately. In this case, you can cancel the ongoing replica migration task and perform the emergency task with priority.

1. Log in to the target tenant.

   Here is an example:

   obclient -h172.30.xxx.xxx -P2883 -uroot@tenant1#obdemo -pxxxx -A
   

   For more information about how to connect to a database, see Overview (MySQL mode) or Overview (Oracle mode).

2. Query the ongoing replica task.

   • sys tenant

     obclient [oceanbase]> SELECT * FROM oceanbase.CDB_OB_LS_REPLICA_TASKS;
     

     For more information about the fields in the CDB_OB_LS_REPLICA_TASKS view, see CDB_OB_LS_REPLICA_TASKS.

   • User tenant

     MySQL mode

     Oracle mode

     Execute the following statement in MySQL mode:

     obclient [oceanbase]> SELECT * FROM oceanbase.DBA_OB_LS_REPLICA_TASKS;
     

     Execute the following statement in Oracle mode:

     obclient [SYS]> SELECT * FROM SYS.DBA_OB_LS_REPLICA_TASKS;
     

     A sample query result is as follows:

     +-------+-----------------+------------------------------------+-------------+----------+-----------------------+-------------------------+-----------------------------+---------------------+-----------------------+-------------------------+-----------------------------+---------------------+--------------------+----------------------+-----------+------------------+--------------------+---------------------+---------------------+---------------------+---------------------------------------------+
     | LS_ID | TASK_TYPE       | TASK_ID                            | TASK_STATUS | PRIORITY | TARGET_REPLICA_SVR_IP | TARGET_REPLICA_SVR_PORT | TARGET_PAXOS_REPLICA_NUMBER | TARGET_REPLICA_TYPE | SOURCE_REPLICA_SVR_IP | SOURCE_REPLICA_SVR_PORT | SOURCE_PAXOS_REPLICA_NUMBER | SOURCE_REPLICA_TYPE | DATA_SOURCE_SVR_IP | DATA_SOURCE_SVR_PORT | IS_MANUAL | TASK_EXEC_SVR_IP | TASK_EXEC_SVR_PORT | CREATE_TIME         | START_TIME          | MODIFY_TIME         | COMMENT                                     |
     +-------+-----------------+------------------------------------+-------------+----------+-----------------------+-------------------------+-----------------------------+---------------------+-----------------------+-------------------------+-----------------------------+---------------------+--------------------+----------------------+-----------+------------------+--------------------+---------------------+---------------------+---------------------+---------------------------------------------+
     |  1001 | MIGRATE REPLICA | Y13CE64586BD4-000610C5F3EDBBCB-0-0 | INPROGRESS  | LOW      | 100.xx.xxx.002        |                    5072 |                           2 | FULL                | 100.xx.xxx.003        |                    5073 |                           2 | FULL                | 100.xx.xxx.003     |                 5073 | FALSE     | 100.xx.xxx.002   |               5072 | 2024-02-07 15:23:04 | 2024-02-07 15:23:04 | 2024-02-07 15:23:04 | migrate replica due to unit group not match |
     +-------+-----------------+------------------------------------+-------------+----------+-----------------------+-----------------------  +-----------------------------+---------------------+-----------------------+-------------------------+-----------------------------+---------------------+--------------------+----------------------+-----------+------------------+--------------------+---------------------+---------------------+---------------------+---------------------------------------------+
     1 row in set
     

     The query result shows that the replica task with the task type of MIGRATE REPLICA is in progress. Record the task ID of the task.

     For more information about the fields in the DBA_OB_LS_REPLICA_TASKS view, see DBA_OB_LS_REPLICA_TASKS.

3. Execute the ALTER SYSTEM CANCEL REPLICA TASK statement to cancel the ongoing replica task.

   The syntax is as follows:

   ALTER SYSTEM CANCEL REPLICA TASK TASK_ID [=] 'task_id' [TENANT [=] 'tenant_name'];
   

   The parameters in the syntax are described as follows:

   • task_id: the task ID of the replica task to be canceled.

   • tenant_name: the name of the target tenant. You can specify another tenant in the sys tenant and specify only the current tenant in a user tenant. If this parameter is not specified, the name of the current tenant is used. You cannot use the all, all_user, or all_meta option in this statement to specify all tenants, all user tenants, or all meta tenants.

   • This statement cancels only one replica task of the tenant at a time.

   Here is an example:

   obclient> ALTER SYSTEM CANCEL REPLICA TASK TASK_ID = 'Y13CE64586BD4-000610C5F3EDBBCB-0-0';
   

4. Check whether the replica task is canceled.

   • sys tenant

     obclient [oceanbase]> SELECT * FROM oceanbase.CDB_OB_LS_REPLICA_TASK_HISTORY WHERE TASK_ID = 'Y13CE64586BD4-000610C5F3EDBBCB-0-0';
     

     For more information about the fields in the CDB_OB_LS_REPLICA_TASK_HISTORY view, see CDB_OB_LS_REPLICA_TASK_HISTORY.

   • User tenant

     MySQL mode

     Oracle mode

     Execute the following statement in MySQL mode:

     obclient [oceanbase]> SELECT * FROM oceanbase.DBA_OB_LS_REPLICA_TASK_HISTORY WHERE TASK_ID = 'Y13CE64586BD4-000610C5F3EDBBCB-0-0';
     

     Execute the following statement in Oracle mode:

     obclient [SYS]> SELECT * FROM SYS.DBA_OB_LS_REPLICA_TASK_HISTORY WHERE TASK_ID = 'Y13CE64586BD4-000610C5F3EDBBCB-0-0';
     

     A sample query result is as follows:

     +-------+-----------------+------------------------------------+-------------+----------+-----------------------+-------------------------+-----------------------------+---------------------+-----------------------+-------------------------+-----------------------------+---------------------+--------------------+----------------------+-----------+------------------+--------------------+---------------------+---------------------+---------------------+---------------------+-------------------------------------------------------------------------------------------------+---------------------------------------------+
     | LS_ID | TASK_TYPE       | TASK_ID                            | TASK_STATUS | PRIORITY | TARGET_REPLICA_SVR_IP | TARGET_REPLICA_SVR_PORT | TARGET_PAXOS_REPLICA_NUMBER | TARGET_REPLICA_TYPE | SOURCE_REPLICA_SVR_IP | SOURCE_REPLICA_SVR_PORT | SOURCE_PAXOS_REPLICA_NUMBER | SOURCE_REPLICA_TYPE | DATA_SOURCE_SVR_IP | DATA_SOURCE_SVR_PORT | IS_MANUAL | TASK_EXEC_SVR_IP | TASK_EXEC_SVR_PORT | CREATE_TIME         | START_TIME          | MODIFY_TIME         | FINISH_TIME         | EXECUTE_RESULT                                                                                  | COMMENT                                     |
     +-------+-----------------+------------------------------------+-------------+----------+-----------------------+-------------------------+-----------------------------+---------------------+-----------------------+-------------------------+-----------------------------+---------------------+--------------------+----------------------+-----------+------------------+--------------------+---------------------+---------------------+---------------------+---------------------+-------------------------------------------------------------------------------------------------+---------------------------------------------+
     |  1001 | MIGRATE REPLICA | Y13CE64586BD4-000610C5F3EDBBCB-0-0 | CANCELED    | LOW      | 100.xx.xxx.002        |                    5072 |                           2 | FULL                | 100.xx.xxx.003        |                    5073 |                           2 | FULL                | 100.xx.xxx.003     |                 5073 | FALSE     | 100.xx.xxx.002   |               5072 | 2024-02-07 15:54:35 | 2024-02-07 15:54:31 | 2024-02-07 15:54:35 | 2024-02-07 15:54:34 | ret:-4072, OB_CANCELED; elapsed:4109659; comment:[storage] receive task reply from storage rpc; | migrate replica due to unit group not match |
     +-------+-----------------+------------------------------------+-------------+----------+-----------------------+-------------------------+-----------------------------+---------------------+-----------------------+-------------------------+-----------------------------+---------------------+--------------------+----------------------+-----------+------------------+--------------------+---------------------+---------------------+---------------------+---------------------+-------------------------------------------------------------------------------------------------+---------------------------------------------+
     1 row in set
     

     The query result shows that the status of the task is CANCELED.

     For more information about the fields in the DBA_OB_LS_REPLICA_TASK_HISTORY view, see DBA_OB_LS_REPLICA_TASK_HISTORY.

References

• Add replicas

• Remove replicas

• Convert the type of a replica

• Modify the number of Paxos replicas of a log stream

• Migrate replicas