Restart a node

Restarting a node is a common O&M action. It is suitable for brief maintenance of a server or when a system configuration item is modified and a restart is needed for the modification to take effect. The downtime of a node during a restart must be shorter than the time specified in the server_permanent_offline_time parameter. Otherwise, the node will be permanently offline. If the maintenance of a server lasts a long time, you must replace the server. For more information, see Replace a node.

Background information

As a distributed database, OceanBase Database is typically deployed with multiple replicas (for example, three replicas in a geo-redundant deployment with three IDCs in one region or five replicas in a geo-disaster recovery deployment with three IDCs in two regions). The Paxos protocol is used to achieve majority consensus among the replicas during transaction commit to maintain data consistency among replicas, and to ensure RPO=0 SLA in the case of failures of minority replicas.

The STOP SERVER command achieves lossless restart in a multi-replica architecture. The STOP SERVER command performs the following operations:

1. It strips all leaders from the server to be restarted and ensures that the replicas on other servers (excluding the server to be restarted) achieve majority.

2. It uses the Root Service to mark the server to be restarted as stopped (node status is ACTIVE and stop_time is greater than 0). After a client recognizes this status, it will not route business requests to the server.

After the server is successfully stopped, future restarts of the server will not trigger leader elections or cause errors in clients, ensuring the transparency of the operation to business traffic. If the STOP SERVER command fails to execute, you need to stop the restart and check the cause. Some possible causes are insufficient replicas, redo log latency, and the total number of voting members being less than the majority.

Procedure

The major steps to restart a node are: stop services, perform a minor compaction, shut down the process, start the process, and start services.

This topic provides guidance on how to restart a node in a cluster. If you want to restart multiple nodes, you can perform the same operation multiple times.

1. Log in to the sys tenant of the cluster as the root user.

   Note that you must specify the corresponding parameters in the following sample code based on your database connection details.

   obclient -h10.xx.xx.xx -P2883 -uroot@sys#obdemo -p***** -A
   

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

2. Run the following command to isolate the node to be restarted.

   During the restart of a node, the service continuity may be interrupted. For example, if the cluster contains only one or two nodes or the data of a tenant is distributed on only two nodes, the system cannot provide services during the restart of the node. The Stop Server operation ensures that the interruption to service continuity is minimized. After the node is isolated, it will no longer provide services. If the Stop Server operation fails, check the deployment of the cluster or resolve the problem based on the error message, and then retry the operation. Alternatively, if the service interruption can be accepted, skip this step.

   obclient [(none)]> ALTER SYSTEM STOP SERVER 'svr_ip:svr_port';
   

   The parameters are described as follows:

   • svr_ip: the IP address of the node to be stopped.

   • svr_port: the RPC port of the node to be stopped. The default value is 2882.

   Here is an example:

   obclient [(none)]> ALTER SYSTEM STOP SERVER '172.xx.xx.xx:2882';
   

   After the execution is successful, query the STATUS column of the oceanbase.DBA_OB_SERVERS view for the server that was stopped. You will find that the value of this column remains ACTIVE but the value of the STOP_TIME column changes from NULL to the time when the service was stopped.

   For more information about how to query the oceanbase.DBA_OB_SERVERS view, see View a node.

3. Run the following command to perform a minor compaction on the node to be restarted. This will shorten the time required for redo log replay after the node is restarted and accelerate the restart process.

   obclient [(none)]> ALTER SYSTEM MINOR FREEZE SERVER = ('svr_ip:svr_port');
   

   The parameters are described as follows:

   • svr_ip: the IP address of the node to be restarted.

   • svr_port: the RPC port of the node to be restarted. The default value is 2882.

   Here is an example:

   obclient [(none)]> ALTER SYSTEM  MINOR FREEZE SERVER = ('172.xx.xx.xx:2882');
   

   After the minor compaction is completed, proceed to the next step. For more information about how to check the minor compaction progress, see View minor compaction information.

   For more information about minor compactions, see Major and minor compactions.

4. Stop the observer process.

   1. Log in to the server where the process to be stopped is located as the admin user.

   2. Use the CLI tool to navigate to the /home/admin/oceanbase directory of the server.

      [admin@xxx /]$ cd /home/admin/oceanbase
      

      For more information about the installation directories of OceanBase Database, see OBServer installation directory structure.

   3. Run the following command to view and obtain the process ID of the node.

      [admin@xxx oceanbase]$ ps -ef | grep observer | grep -v grep
      admin    103364      1 99  2022 ?        51-17:24:41 /home/admin/oceanbase/bin/observer
      

      In this example, 103364 is the process ID of the node.

   4. Stop the observer process.

      The command is as follows:

      [admin@xxx oceanbase]$ kill -9 pid
      

      Here, pid is the observer process ID of the node to be stopped.

      Here is an example:

      [admin@xxx oceanbase]$ kill -9 103364
      

      Notice

      You can stop only one observer process in a deployment directory. If you want to stop observer processes on multiple nodes, you need to log in to each server in sequence.

   5. Run the following command to check whether the process has stopped.

      [admin@xxx oceanbase]$ ps aux | grep observer
      

      If no information is returned after the command execution, the process has been stopped successfully.

5. (Optional) If you want to perform maintenance on the server, perform the maintenance in this step.

6. Start the observer process.

   1. Log in to the server where the process to be started is located as the admin user.

   2. Start the observer process.

      [admin@xxx oceanbase]$ cd /home/admin/oceanbase  &&  ./bin/observer
      

      Notice

      You can start only one observer process in a deployment directory. If you want to start observer processes on multiple nodes, you need to log in to each server in sequence.

      For more information about the installation directories of OceanBase Database, see OBServer installation directory structure.

      If the observer process starts successfully, the value of the START_SERVICE_TIME column in the oceanbase.DBA_OB_SERVERS view changes from NULL to the time when the service is started.

7. Run the following command to start the services of the node.

   obclient [(none)]> ALTER SYSTEM START SERVER 'svr_ip:svr_port';
   

   where:

   • svr_ip: the IP address of the node.

   • svr_port: the RPC port of the node. The default value is 2882.

   Here is an example:

   obclient [(none)]> ALTER SYSTEM START SERVER '172.xx.xx.xx:2882';
   

   After the execution is successful, query the STOP_TIME column of the oceanbase.DBA_OB_SERVERS view. You will find that the value of this column is NULL, indicating that the node has started services and can provide services.

   For more information about how to query the oceanbase.DBA_OB_SERVERS view, see View a node.

References

For more information about node O&M, see the following topics:

• View a node

• Add a node

• Delete a node

• Isolate a node

• Replace a node