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Updated at: Apr 02, 2022 GMT+08:00

Creating a Read Replica


Read replicas are used to enhance the read capabilities and reduce the load on primary DB instances.

You can create read replicas as needed.

A maximum of five read replicas can be created for a primary DB instance.

The specifications of read replicas must be greater than or equal to the specifications of the current primary DB instance.


  1. Log in to the management console.
  2. Click in the upper left corner and select a region and a project.
  3. Click in the upper left corner of the page and choose Database > Relational Database Service. The RDS console is displayed.
  4. On the Instance Management page, locate the target DB instance and choose More > Create Read Replica in the Operation column.

    Alternatively, click the target DB instance. In the DB instance topology, click under the primary DB instance to create read replicas.

  5. On the displayed page, configure information about the DB instance and click Next.

    Table 1 Basic information




    By default, read replicas are in the same region as the primary DB instance.

    DB Instance Name

    Different DB instances can have the same name. The instance name must start with a letter and consist of 4 to 64 bytes. Only letters (case-sensitive), digits, hyphens (-), and underscores (_) are allowed.

    DB Engine

    Same as the DB engine of the primary DB instance by default and cannot be changed.

    DB Engine Version

    Same as the DB engine version of the primary DB instance by default and cannot be changed.


    RDS allows you to deploy primary DB instances and read replicas in a single AZ or across AZs to improve reliability.

    Table 2 Instance specifications



    Instance Class

    Refers to the CPU and memory of a DB instance. Different instance classes have different numbers of database connections and maximum IOPS.

    After a DB instance is created, you can change its CPU and memory. For details, see Changing a DB Instance Class.

    DB instances in a DCC only support the general-enhanced instance class.

    Storage Type

    Determines the DB instance read/write speed. The higher the maximum throughput is, the higher the DB instance read/write speed can be.

    • Ultra-high I/O: supports a maximum throughput of 350 MB/s.
    • Cloud SSD: stores data in cloud SSDs to achieve decoupled compute and storage.
    • If you select DSS for Resource Type, only the storage type that you have selected when buying the DSS service is displayed by default.

    Storage Space

    Contains the file system overhead required for inode, reserved block, and database operation.

    By default, storage space of a read replica is the same as that of the primary DB instance.

    Disk Encryption

    • Disable: indicates the encryption function is disabled.
    • Enable: indicates the encryption function is enabled. Security is improved but system performance is affected.

      Key Name: indicates the tenant key. You can select an existing key or create a new one.

      • Once the DB instance is created, you cannot modify the disk encryption status or change the key. The backup data stored in OBS is not encrypted.
      • After an RDS DB instance is created, do not disable or delete a key that is currently in use. Otherwise, RDS will be unavailable and data cannot be restored.
      • For details about how to create a key, see the "Creating a CMK" section in the Data Encryption Workshop User Guide.
    Table 3 Network




    Same as the primary DB instance's VPC.


    Same as the primary DB instance's subnet. A floating IP address is automatically assigned when you create a read replica. You can also enter an unused floating IP address in the subnet CIDR block. After the read replica is created, you can change the floating IP address.

    Security Group

    Same as the primary DB instance's security group.

  6. Confirm specifications.

    • If you need to modify your settings, click Previous.
    • If you do not need to modify your settings, click Submit.

  7. After a read replica has been created, you can view and manage it on the Instance Management page by clicking on the left of the DB instance to which it belongs.

    Alternatively, click the target DB instance. In the DB instance topology, click the name of the target read replica. You can view and manage it in the displayed pane.

    You can view the detailed progress and result of the task on the Task Center page. For details, see Task Center.

Follow-up Operations

Managing a Read Replica

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