ApsaraDB RDS for SQL Server enforces the following limits to maintain instance stability and security. Review feature availability and database count limits before you provision or upgrade an instance.
Feature support by edition
The table below shows feature availability across RDS editions and SQL Server versions. Features marked Supported\* have conditions — see the notes after the table.
| Feature | RDS Cluster Edition | RDS High-availability Edition | RDS High-availability Edition (2008 R2) | RDS Basic Edition |
|---|---|---|---|---|
| SQL Server versions | 2025 EE / 2022 EE / 2019 EE / 2017 EE | 2025 SE / 2022 SE / 2019 SE / 2017 SE / 2016 SE/EE / 2014 SE/EE / 2012 SE/EE | 2008 R2 | 2025 SE/EE / 2022 Web/SE/EE / 2019 Web/SE/EE / 2017 Web/SE/EE / 2016 Web/SE/EE / 2014 SE / 2012 Web/EE (single-node) |
| Max databases | 300 (formula-based) | 300 (formula-based) | 50 | 400 (formula-based) |
| Max database accounts | Unlimited | Unlimited | 500 | Unlimited |
| Max client connections | Unlimited | Unlimited | Depends on the instance type | Unlimited |
| Create users, logins, or databases | Supported | Supported | Supported | Supported |
| Database-level DDL triggers | Supported | Supported | Not supported | Supported |
| Authorization within databases | Supported | Supported | Not supported | Supported |
| Terminate threads | Supported | Supported | Supported | Supported |
| Linked Server | Supported\* | Supported\* | Not supported | Not supported |
| Distributed transaction | Supported | Supported | Not supported | Not supported |
| SQL Profiler | Supported | Supported | Supported | Supported |
| Tuning Advisor | Supported | Supported | Not supported | Supported |
| Change data capture (CDC) | Supported | Supported (not supported for 2012 SE) | Supported for cloud disks; not supported for Premium Local SSDs | Not supported |
| Change tracking | Supported | Supported | Not supported | Supported |
| Windows domain account logon | Supported\* | Supported\* | Not supported | Not supported |
| SQL Server Integration Services (SSIS) | Supported\* | Supported\* | Not supported | Supported\* |
| SQL Server Analysis Services (SSAS) | ||||
| SQL Server Reporting Services (SSRS) | ||||
| Asynchronous messaging | Supported | Supported | Supported | Supported |
| Database Mail | Supported† | Supported† | Not supported | Supported† |
| R Services | ||||
| Common Language Runtime (CLR) integration | ||||
| Replication | ||||
| Policy Management |
**\* Condition — shared instance family:** Linked Server, Windows domain account logon, and SQL Server Integration Services (SSIS) are not available on instances that use the shared instance family.
† Condition — Database Mail prerequisites: Before using Database Mail, create a host account and a System Admin (SA) account for the instance.
Maximum number of databases
The database limit for SQL Server 2008 R2 instances is fixed at 50. For all other versions, the limit depends on the instance type.
RDS Cluster Edition and RDS High-availability Edition
Formula: min(floor(√CPU cores) × 50, 300)
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Take the square root of the number of CPU cores.
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Round down to the nearest integer.
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Multiply by 50.
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The result, capped at 300, is the maximum number of databases.
Example: A 4-core instance running SQL Server 2016 Standard Edition supports up to floor(√4) × 50 = 2 × 50 = 100 databases.
RDS Basic Edition
Formula: min(floor(√CPU cores) × 100, 400)
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Take the square root of the number of CPU cores.
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Round down to the nearest integer.
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Multiply by 100.
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The result, capped at 400, is the maximum number of databases.
Example: A 4-core instance running SQL Server 2019 Standard Edition supports up to floor(√4) × 100 = 2 × 100 = 200 databases.
Theminfunction returns the smaller of two values. For example,min(100, 300)is 100.