Overview of Changing the Deployment Model

To meet various service requirements, GaussDB allows you to change the instance deployment model. Currently, the following deployment models are supported:

A single-replica primary/standby instance can be changed into a 1 primary + 2 standby instance or a 1 primary + 1 standby + 1 log instance. For details, see Changing the Deployment Model of a Single-Replica Instance (Primary/Standby). Note that rollback is not supported after the deployment model of a single-replica instance is changed.
A standby DN can be changed into a log node in a distributed instance. For details, see Changing Standby DNs to Log Nodes (for a Distributed Instance). The log node is used only to store logs and does not incur fees, which reduces costs and resource consumption. During the change, services will be interrupted for about 1 minute. So, change the deployment model during off-peak hours.

Deployment Model Change Principle of a Single-Replica Primary/Standby Instance

Changing a single-replica instance into a 1 primary + 2 standby instance: In this case, two standby nodes will be added after the change.
Figure 1 Changing a single-replica instance into a 1 primary + 2 standby instance
Changing a single-replica instance into a 1 primary + 1 standby + 1 log instance: In this case, one standby node and one log node will be added after the change.
Figure 2 Changing a single-replica instance into a 1 primary + 1 standby + 1 log instance

Deployment Model Change Principle of a Distributed Instance

Changing the standby DN into a log node: A 1 primary + 2 standby instance is changed into a 1 primary + 1 standby + 1 log instance. After the change, one standby DN of all shards is changed into a log node.
Figure 3 Changing the standby DN into a log node