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:

For centralized instances, a single-replica 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 (Centralized). Note that rollback is not supported after the deployment model of a single-replica instance is changed.
For distributed instances, a standby DN can be changed into a log node. For details, see Changing Standby DNs to Log Nodes (for a Distributed Instance). The log node is only used 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 Centralized 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 standby DNs to log nodes: Before the change, each shard of the instance has one primary DN and two standby DNs. After the change, one of the standby DNs in each shard is changed to a log node.
Figure 3 Changing standby DNs into log nodes