Restart a node

Restart is a common O&M action that is used for brief maintenance of servers and to restart the system after modifying system configuration items. If the duration of the restart is within the value specified by the cluster-level parameter server_permanent_offline_time, the node will not be permanently offline. Otherwise, the node will be permanently offline. If the server needs a long-term maintenance, 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 region with three IDCs, or five replicas across three regions with five IDCs). The Paxos protocol is used to achieve majority consensus among the replicas during transaction commit to maintain data consistency among replicas. If an exception occurs in the minority of replicas, the system can still meet the SLA of RPO=0.

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

1. Removes all leaders from the restart node and ensures that the majority of replicas is reached on other nodes.

2. Marks the restart node as stopped (with the node status being ACTIVE and the stop_time field greater than 0) in the Root Service. The client identifies the node and will not route business requests to the node.

After the STOP SERVER command executes successfully, the restart node becomes transparent to the business traffic, and no leader election or client errors occur. If the STOP SERVER command execution fails, the restart is stopped, and you need to check the cause. Some possible causes include insufficient replicas, delayed redo logs, and fewer than the majority of voting members.

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 the procedure to restart one 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 actual database configurations.

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

   For more information about how to connect to a 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 a cluster has 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 a 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, you can perform the operation again or skip this step if you can accept the interruption to service continuity.

   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 status of the server. You will find that the value of this column remains ACTIVE unchanged, but the value of the STOP_TIME column changes from NULL to the time when the service is 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 speed up 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 command-line 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

      Only one observer process can be stopped 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 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

      Only one observer process can be started 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.

      After the execution is successful, query the START_SERVICE_TIME column of the oceanbase.DBA_OB_SERVERS view. If this value is not NULL, the observer process has been started successfully.

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. If this value is NULL, the node has started services and is ready to 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