ApsaraDB RDS:Create a read-only ApsaraDB RDS for SQL Server instance

Prerequisites

Read-only RDS instances can be created only for primary RDS instances that meet the following requirements:

• Instance version: SQL Server 2017 EE on RDS Cluster Edition, SQL Server 2019 EE on RDS Cluster Edition, or SQL Server 2022 EE on RDS Cluster Edition

• Instance edition: Cluster Edition

• Instance storage type: Enterprise SSD (ESSD), premium performance disk

• Billing method: Subscription or pay-as-you-go (Serverless ApsaraDB RDS for SQL Server instances are not supported)

Usage notes

• You can create read-only RDS instances for a primary RDS instance. You cannot convert existing primary RDS instances to read-only RDS instances.

• When you create a read-only RDS instance, the system replicates data from the secondary RDS instance to the read-only RDS instance. This prevents interruptions to your workloads on the primary RDS instance.

• Number of read-only RDS instances: You can create up to seven read-only RDS instances for a primary RDS instance.

• Instance backup: You cannot configure backup policies or manually create backups for read-only RDS instances. These are configured and created on the primary RDS instance. You cannot create temporary RDS instances from backup files or any point in time. You cannot overwrite RDS instances by using backup sets. After a read-only RDS instance is created, you cannot use backup sets to overwrite the primary RDS instance to restore data.

• Data migration: You cannot migrate data to read-only RDS instances.

• Database management: You cannot create or delete databases on read-only RDS instances.

• Account management: You cannot create or delete accounts, grant permissions to accounts, or change the passwords of accounts on read-only RDS instances.

• Instance creation time: The time required to create a read-only RDS instance correlates directly with the data volume and I/O performance of the primary RDS instance. Before creating a read-only RDS instance, we recommend evaluating and optimizing the data volume and I/O performance of the primary RDS instance to shorten the creation time.

• Storage space: The storage space of a read-only instance cannot be less than that of the primary instance.

Billing rules

You are charged for the read-only RDS instances that you create based on the subscription billing method or the pay-as-you-go billing method. For more information, see Pricing.

Create a read-only RDS instance

You can create a read-only instance in the RDS console or by calling the CreateReadOnlyDBInstance API.

1. Log on to the ApsaraDB RDS console and go to the Instances page. In the top navigation bar, select the region in which the RDS instance resides. Then, find the RDS instance and click the instance ID.

2. In the Instance Distribution section, to the right of Read-only Instance, click Add.

   

3. Configure the basic resources, including the billing method, storage class, and zone. Then, click Next: Instance Configuration.

   1. Select the Billing Method.

      Billing Method	Recommendations	Benefit
      Subscription	A subscription instance is an instance for which you pay an upfront fee. If you want to use an instance for a long period of time, we recommend that you select the Subscription billing method. If you select the subscription billing method, configure the Subscription Duration parameter in the lower part of the page.	For long-term use, the subscription billing method is more cost-effective than the pay-as-you-go billing method. You are offered lower prices for longer subscription durations.
      Pay-as-you-go	You are charged on an hourly basis for a pay-as-you-go instance based on your actual resource usage. If you want to use an RDS instance for a short period of time, we recommend that you select the Pay-as-you-go billing method. You can create a Pay-as-you-go instance. After you confirm that the created instance meets your business requirements, you can change the billing method of the instance to subscription.	You can release an instance at any time. The billing stops immediately after you release the instance.

   2. Configure the Storage Type parameter.

      For more information, see Storage classes.

   3. Select the Zone for the instance.

      Note

      • Each zone is an independent physical location within a region. No substantive differences exist between zones in the same region.

      • If the RDS instance resides in the same zone as the Elastic Compute Service (ECS) instance on which your application is deployed, these instances can deliver optimal performance. If the RDS instance and the ECS instance reside in different zones in the same region, the performance is slightly lower than when they reside in the same zone.

   4. Select the Instance Type.

      Specify the category (dedicated or general-purpose instance family). Then, specify the CPU cores, memory capacity, and maximum number of connections.

      Category	Description	Benefit
      General-purpose Instance Types	Dedicated: memory and I/O Shared: CPU and storage	Low cost and cost-effective.
      Dedicated Instance Types	A dedicated RDS instance occupies all the allocated CPU, memory, storage, and I/O resources. Note The dedicated host instance family is the highest configuration of the dedicated instance family. A dedicated host RDS instance exclusively occupies all the CPU, memory, storage, and I/O resources of the host on which the RDS instance is deployed.	A dedicated instance provides better performance and stability.

      Note

      • Each instance type has a specific number of CPU cores, memory, maximum connections, and maximum IOPS.

      • To ensure I/O performance for data synchronization, we recommend ensuring the memory capacity of the read-only RDS instance is equal to or greater than the memory capacity of the primary RDS instance.

   5. Configure the Storage Capacity parameter.

      The storage capacity includes data space, system file space, log file space, and transaction file space. The storage capacity range (minimum and maximum values) depends on the instance type and storage type you selected earlier. You can adjust the storage capacity in increments of at least 5 GB.

      Note

      • The storage capacity of a read-only RDS instance cannot be less than the storage capacity of the primary RDS instance.

      • The storage space of some local SSDs is tied to the instance type, but this restriction does not apply to enterprise SSDs (ESSDs) or standard SSDs.

4. Configure instance resources, such as the network type, vSwitch, and resource group. Then, click Next:Confirm Order.

   1. Network Type is fixed to VPC.

   2. Select VPC and vSwitch of Primary Node.

      We recommend selecting the VPC in which your ECS instance resides for the RDS instance. If the RDS instance and the ECS instance reside in different VPCs, these instances cannot communicate over an internal network.

      Note

      You can connect the RDS instance and the ECS instance over an internal network even if the instances use different vSwitches in the same VPC.

   3. Configure custom parameters. If you do not have special business requirements, you can retain the default values of these parameters.

      Parameter	Description
      Release Protection	If you set Billing Method to Pay-as-you-go, you can enable the release protection feature to prevent accidental release of the instance.
      Resource Group	You can use the default resource group or select a custom resource group as needed.
      Instance Name	The value must be 2 to 255 characters in length and can contain letters, digits, underscores (_), and hyphens (-). It must start with a letter or Chinese character.
      Character Set Collation Rule	The default is the system character set collation of the primary instance.

5. Confirm the Parameter Configuration, Quantity, and Subscription Duration (for subscription instances only), click Confirm Order, and complete the payment.

   Note

   • For subscription instances, we recommend selecting Auto-renewal. This prevents service interruptions if you forget to renew your instance.

   • It takes 1 to 10 minutes to create an instance. You can refresh the page to view the instance.

View a read-only RDS instance

You can view a read-only RDS instance on the Instances page, the Cluster Management page of the required RDS instance, or the Basic Information page of the required RDS instance.

What to do next

After the read-only instance is created, you need to enable the read-write splitting connection and configure the weight ratio for the read-only address. The system will process read requests based on the configured weight ratio.

FAQs

SELECT
    ag.name AS [availability_group_name]
    , d.name AS [database_name]
    , ar.replica_server_name AS [replica_instance_name]
    , drs.truncation_lsn
    , drs.log_send_queue_size
    , drs.redo_queue_size
FROM
    sys.availability_groups ag
    INNER JOIN sys.availability_replicas ar
        ON ar.group_id = ag.group_id
    INNER JOIN sys.dm_hadr_database_replica_states drs
        ON drs.replica_id = ar.replica_id
    INNER JOIN sys.databases d
        ON d.database_id = drs.database_id
WHERE drs.is_local=0
ORDER BY
    ag.name ASC, d.name ASC, drs.truncation_lsn ASC, ar.replica_server_name ASC