Adding or Deleting a Standby Node

Availability

This feature is available since MogDB 2.0.0.

Introduction

Standby nodes can be added and deleted.

Benefits

If the read pressure of the primary node is high or you want to improve the disaster recovery capability of the database, you need to add a standby node. If some standby nodes in a cluster are faulty and cannot be recovered within a short period of time, you can delete the faulty nodes to ensure that the cluster is running properly.

Description

MogDB can be scaled out from a single node or one primary and multiple standbys to one primary and eight standbys. Cascaded standby nodes can be added. Standby nodes can be added when a faulty standby node exists in the cluster. One primary and multiple standbys can be scaled in to a single node. A faulty standby node can be deleted.

Standby nodes can be added or deleted online without affecting the primary node.

Enhancements

None.

Constraints

For adding a standby node:

• Ensure that the MogDB image package exists on the primary node.
• Ensure that the same users and user groups as those on the primary node have been created on the new standby node.
• Ensure that the mutual trust of user root and the database management user has been established between the existing database nodes and the new nodes.
• Ensure that the XML file has been properly configured and information about the standby node to be scaled has been added to the installed database configuration file.
• Ensure that only user root is authorized to run the scale-out command.
• Do not run the gs_dropnode command on the primary node to delete other standby nodes at the same time.
• Ensure that the environment variables of the primary node have been imported before the scale-out command is run.
• Ensure that the operating system of the new standby node is the same as that of the primary node.
• Do not perform an primary/standby switchover or failover on other standby nodes at the same time.

For deleting a standby node:

• Delete the standby node only on the primary node.
• Do not perform an primary/standby switchover or failover on other standby nodes at the same time.
• Do not run the gs_expansion command on the primary node for scale-out at the same time.
• Do not run the gs_dropnode command twice at the same time.
• Before deletion, ensure that the database management user trust relationship has been established between the primary and standby nodes.
• Run this command as a database administrator.
• Before running commands, run the source command to import environment variables of the primary node.

Dependencies

None.