This topic introduces SQL Server read-only instances. If your application initiates a small number of write requests but a large number of read requests, a single instance may not be able to resist the read pressure. As a result, services may be affected. To achieve the elastic expansion of the read ability and share the pressure of the database, you can create one or more read-only instances in a region. The read-only instances can handle massive read requests and increase the application throughput.
- For RDS SQL Server, only the SQL Server 2017 Cluster (AlwaysOn) Edition supports read-only instances.
- Each read-only instance adopts a single-node architecture (without slave nodes).
The billing method of read-only instances is Pay-As-You-Go. The following table lists the prices of common instances.
Hourly prices of specifications and storage
2-core 4 GB
2-core 8 GB
4-core 8 GB
4-core 16 GB
8-core 16 GB
8-core 32 GB
16-core 64 GB
|China mainland's regions||$0.225||$0.447||$0.459||$0.851||$0.888||$1.732||$3.389||$0.0003/GB|
|China (Hong Kong)||$0.264||$0.522||$0.537||$0.993||$1.035||$2.02||$3.954||$0.0004/GB|
|US (Sillicon Vally)||$0.292||$0.579||$0.595||$1.099||$1.146||$2.237||$4.378||$0.0003/GB|
FeaturesRead-only instances offer the following features:
- Account and database management: No account or database maintenance is required for a read-only instance. Both the account and database are synchronized through the master instance.
- Billing: Read-only instances support billing measured per hour, which is user-friendly and cost-efficient.
- Specifications: The specifications of a read-only instance can differ from those of the master instance, and can be changed at any time. We recommend that the specifications of the read-only instance be equal to or higher than those of the master instance; otherwise the read-only instance may have high latency or workloads.
- Network type: can differ from that of the master instance.
- Whitelist: When a read-only instance is created, it automatically copies the whitelist of the master instance. However, the whitelist of the read-only instance is independent from that of the master instance. You can modify the whitelist of the read-only instance by referring to Configure a whitelist for an RDS for SQL Server instance.
- Monitoring and alarms: Up to 20 system performance monitoring views can be used, which includes disk capacity, IOPS, connections, CPU utilization, and network traffic. Users can view the load of instances at ease.
- Quantity of read-only instances:
Database Quantity SQL Server Up to 7 read-only instances can be created for each master instance.
- Read-only instances do not support backup settings or manual backup.
- Instance recovery:
- Read-only instances do not support the creation of temporary instances through backup files or a point in time. Read-only instances do not support the overwriting of instances using backup sets.
- After creating a read-only instance, the master instance does not support data recovery through the direct overwriting of instances using backup sets.
- You cannot migrate data to read-only instances.
- You cannot create or delete databases for read-only instances.
- You cannot create or delete accounts for read-only instances.
- You cannot authorize accounts or modify account passwords for read-only instances.
Can the accounts on the master instance be used on the read-only instances?
Accounts on the master instance are synchronized to the read-only instances. You can use the accounts to read data from the read-only instances but cannot write data into the read-only instances.