Your choice of instance family determines how CPU, memory, I/O, and storage are allocated to your database instance — and whether those resources are shared with other instances on the same physical server. Getting this decision right is the foundation of stable, cost-effective database operations.
ApsaraDB RDS offers four instance families: shared, general-purpose, dedicated, and dedicated host.
Choose an instance family
| Instance family | Best for | Performance guarantee | Supported databases |
|---|---|---|---|
| Dedicated host | Mission-critical systems where database performance cannot be compromised (finance, e-commerce, government, large- to medium-sized internet businesses) | Highest — exclusively uses all resources of a physical server | RDS for MySQL with Premium Local SSDs only |
| Dedicated | Production workloads that require consistent, predictable performance | High — dedicated CPU, memory, and storage; other instances on the same server cannot affect your performance | MySQL, PostgreSQL, SQL Server, MariaDB |
| General-purpose | Workloads that can tolerate occasional performance variation in exchange for lower cost | Moderate — CPU is shared; performance may drop when the physical server is under high load | — |
| Shared | Non-production or cost-sensitive workloads with low performance requirements | Low — CPU is shared at a higher multiplexing rate than general-purpose; resource contention is possible | SQL Server only |
The dedicated host family is the top-tier configuration within the dedicated family. It dedicates the entire physical server — all CPUs, memory, I/O, and storage — to a single instance.
Resource isolation
Instance families differ in how they isolate CPU, memory, I/O, and storage. Within the same family, the storage type — cloud disk or Premium Local SSD — also affects isolation.
| Instance family | Storage type | CPU | Memory | I/O | Storage |
|---|---|---|---|---|---|
| Dedicated host | — | Dedicated | Dedicated | Dedicated | Dedicated |
| Dedicated | Premium Local SSD | Dedicated | Dedicated | Shared | Dedicated |
| Dedicated | Cloud disk | Dedicated | Dedicated | Dedicated | Dedicated |
| General-purpose | Premium Local SSD | Shared | Shared | Dedicated | — |
| General-purpose | Cloud disk | Shared | — | Dedicated | — |
| Shared | — | Shared | Dedicated | — | — |
How each family handles shared resources:
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Dedicated host — Exclusively uses all four resource types. Provides the highest level of performance stability and isolation.
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Dedicated — CPU and memory are always dedicated. I/O is dedicated when using cloud disk, shared when using Premium Local SSD. Other instances on the same physical server cannot affect your performance.
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General-purpose — CPU is shared with other instances on the same physical server, at a lower multiplexing rate than the shared family. Performance may fluctuate under high load.
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Shared — CPU is shared at a higher multiplexing rate. Cost-effective, but carries a higher risk of resource contention than general-purpose.
Change instance families
Select an instance family when you purchase an instance. You can change it afterward, subject to the following limits.
Switching between general-purpose and dedicated (including dedicated host) is supported. For instructions, see the change specifications topics for your database engine:
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Change the specifications of an ApsaraDB RDS for MySQL instance
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Change the specifications of an ApsaraDB RDS for SQL Server instance
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Change the specifications of an ApsaraDB RDS for PostgreSQL instance
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Change the specifications of an ApsaraDB RDS for MariaDB instance
Switching between shared and any other family is not supported directly. To migrate off the shared family:
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Purchase a new instance using the target instance family.
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Use Data Transmission Service (DTS) to migrate data from the shared instance to the new instance.
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Switch your workloads to the new instance during off-peak hours.
What's next
For a full list of instance types and their specifications, see Primary instance types and Read-only instance types.
FAQ
Why do general-purpose instances appear to have higher specifications than dedicated instances?
General-purpose instance specs represent the theoretical peak performance — the maximum the instance can reach when the physical server has spare capacity. That peak is not guaranteed for extended periods and will drop under high load. Dedicated instance specs represent a guaranteed baseline: a stable performance level that is not affected by other instances on the same physical server. For production systems, that predictability is typically more valuable than a higher but uncertain peak.