DB Instance Types

Table 1 lists the instance types of GaussDB.

**Table 1** Instance types
Instance Type	Deployment Model	Scale-out Supported	Application Scenario	Component	Service Processing
Distributed	Independent deployment: Database components are deployed on different nodes. This model is suitable for where high reliability and stability are required and the instance scale is large. Combined: 3-node deployment where there are three shards and each shard contains one primary DN and two standby DNs.	Yes	The data volume is large, and large data capacity and high concurrency are required.	OM CM GTM ETCD CN DN	An application sends a SQL query request to a CN. The CN uses the optimizer of the database to generate an execution plan and sends the plan to DNs. Each DN processes data based on the execution plan. After the processing is complete, DNs return the result set to the CN for summary. Finally, the CN returns the summary result to the application.
Primary/Standby	HA (1 primary + 2 standby): 3-node deployment where there is a shard. The shard contains one primary DN and two standby DNs. Single replica: single-node deployment where there is only one CMS component and one DN. This deployment model is not suitable for production environments. To create a single-replica instance, ensure that the instance version is 2.2 or later. The availability (SLA) cannot be guaranteed because the instance is deployed on a single server. 1 primary + 1 standby + 1 log: 3-node deployment where there is a shard. The shard contains one primary DN, one standby DN, and one log-dedicated DN.	No	The data volume is small and stable, and data reliability and service availability are extremely important.	OM CM ETCD DN	An application sends a task directly to the DN, and the DN returns the result to the application after processing the task.

OM: The Operation Manager (OM) provides management APIs and tools for routine maintenance and configuration management of the cluster.
CM: The Cluster Manager (CM) manages and monitors the running status of functional units and physical resources in a distributed system, ensuring stable running of the entire system.
GTM: The Global Transaction Manager (GTM) generates and maintains the global transaction IDs, transaction snapshots, timestamps, and sequences that must be unique globally.
ETCD: The editable text configuration daemon (ETCD) is used for shared configuration and service discovery (service registry and search).
CN: A CN receives access requests from applications and returns execution results to clients. It also splits and distributes tasks to different DNs for parallel processing.
DN: A DN stores service data, performs data queries, and returns execution results.

The following figure shows the logical architecture of a distributed GaussDB instance.

Figure 1 Logical architecture of a distributed instance