The instance family of an instance defines the computing capacity, resource isolation level, and performance stability of the instance, which affect the instance performance and cost. Selecting an instance family that is applicable to your business is fundamental to ensuring stable business operations.
Overview
ApsaraDB RDS provides four instance families: shared, general-purpose, dedicated, and dedicated host.
Instance family | Description | Supported databases | Scenarios |
Dedicated host | Fully dedicates all resources of a physical server. This is the top-tier configuration of the dedicated instance family. | Supported only by RDS for MySQL instances that use Premium Local SSDs | Scenarios in which the database is a core system, such as in finance, e-commerce, government, and large- to medium-sized Internet business. |
Dedicated | Dedicates most resources to ensure long-term performance stability. Performance is not affected by other instances on the same physical machine. |
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General-purpose | Utilizes resource multiplexing to balance cost and performance stability. The CPU resource multiplexing rate is lower than that of shared instances. | Application scenarios that have low requirements for performance stability or require a balance between performance and cost. | |
Shared | Maximizes CPU utilization through resource multiplexing. This family is cost-effective but poses a risk of resource contention. | SQL Server only | Scenarios that have low requirements for performance stability and prioritize cost-effectiveness. |
Resource multiplexing and performance stability
Instance families differ in the isolation of CPU, memory, I/O, and storage resources. Within the same instance family, the storage type (cloud disk and Premium Local SSD) also affects resource multiplexing.
Instance family | Resource type | Performance stability | ||||
CPU | I/O | Memory | Storage | |||
Dedicated host | Exclusively uses all four resource types | Provides the highest level of performance stability and isolation. | ||||
Dedicated | Premium Local SSD | Dedicated | Shared | Dedicated | Ensures long-term performance stability. Performance is not affected by other instances on the same physical server. | |
Cloud disk | Exclusively uses all four resource types | |||||
General-purpose | Premium Local SSD | Shared | Dedicated | Shared | Performance may fluctuate when the physical machine is under high load. | |
Cloud disk | Shared | Dedicated | ||||
Shared | Shared | Dedicated | ||||
Change instance families
RDS allows you to select an instance family when you purchase an instance. You can also change the instance family after the purchase. The following limits apply when you change an instance family:
You can switch between the general-purpose and dedicated (including dedicated host) instance families. For more information, see the following topics:
You cannot switch between the shared instance family and other instance families. To change the instance family, you must purchase a new instance that uses a different instance family and then use Data Transmission Service (DTS) to migrate the shared instance to the new instance. Then, switch your workloads over to the new instance during off-peak hours.
Related topics
For a list of instance types and the specifications of each instance type, see Primary instance types and Read-only instance types.
FAQ
Q: Why do general-purpose instances appear to have higher specifications than dedicated instances?
A: The values for general-purpose instances represent the theoretical peak performance, which depends on the available resources in the shared pool and cannot be guaranteed for extended periods. This peak performance can be achieved when the physical machine's resources are idle, but performance may decrease under high load. The values for dedicated instances represent a guaranteed and stable performance level. Although these values may sometimes appear lower, they represent a long-term, stable performance baseline that is not affected by external factors. For production systems, predictable and stable performance is typically more important than an uncertain theoretical peak.