All Products
Search

This Product

    PolarDB:PolarDB-X read-only instances

    Document Center

    PolarDB:PolarDB-X read-only instances

    Last Updated:Jun 04, 2026

    Add a read-only instance to a primary instance.

    How it works

    Primary instance data nodes use a Paxos-based, three-replica architecture for high availability. Read-only instance data nodes add Learner replicas for physical resource isolation and use a global clock to ensure strong data consistency for read-only queries.

    Considerations

    • A read-only instance and its primary instance must be in the same region but can be in different zones.

    • A read-only instance cannot exist independently and must belong to a primary instance. Databases created or deleted on the primary instance are automatically replicated or removed on the read-only instance.

    Procedure

    1. Log on to the PolarDB-X console.

    2. In the top navigation bar, select the region where the instance is deployed.

    3. On the Instances page, click the PolarDB-X 2.0 tab.

    4. In the Operation column of the target instance, click 2023-11-28_133746.png and select Read-only Instance.

      Or, click the instance ID to open the Basic Information page. In the Read-only Instance section on the right, click Create Read-only Instance.

    5. On the purchase page, configure the following parameters:

      Parameter

      Description

      Commodity Type

      Select Subscription or Pay-As-You-Go.

      Note

      • Subscription: prepaid. You pay for the cluster upon creation.

      • Pay-as-you-go: postpaid. You are charged hourly.

      • To create a pay-as-you-go instance, your Alibaba Cloud account balance must be at least 100 USD.

      Region

      Set to the region of the primary instance.

      Primary Node Zone

      Select a zone.

      Network Type

      Set to VPC.

      Virtual Private Cloud

      Select a VPC.

      Note

      • If you do not have a VPC, create a VPC.

      • The VPC of a PolarDB-X read-only instance cannot be changed after creation.

      vSwitch

      Select a vSwitch.

      Note

      • If you do not have a vSwitch, create a vSwitch.

      • You can change the vSwitch after the PolarDB-X read-only instance is created.

      MySQL Version

      This parameter is set to match the Compatibility of the primary instance.

      Edition

      Set to match the primary instance series.

      Type

      Select General-purpose or Dedicated.

      • General-purpose: Multiple PolarDB-X instances share idle computing resources such as CPU on the same hardware, improving cost-effectiveness.

      • Dedicated: A PolarDB-X instance exclusively uses its allocated computing resources such as CPU, delivering more stable performance.

      Compute Node Specifications

      Select compute node specifications.

      Storage Node Specifications

      Select data node specifications.

      Compute Nodes

      Number of compute nodes. Defaults to the primary instance value.

      Storage Nodes

      Number of data nodes. Defaults to the primary instance value.

      Node Specifications

      Resource specifications of the node. Available only for Standard Edition.

      Storage Type

      Set to Local SSD-Custom.

      Note

      Storage capacity does not need to be specified. You are billed hourly based on actual disk usage, rounded up to one hour.

      Subscription Duration

      Select the subscription duration.

      Note

      This parameter is available only when Subscription is set to Subscription.

      Quantity

      Number of instances to purchase.

    6. Click Buy Now.

    7. On the Confirm Order page, read and agree to the terms of service and click Pay to complete the payment.

    8. After payment, wait 10 to 15 minutes for provisioning. View the new read-only instance on the Instances page.

    Related topics

    Read-only columnar instances: PolarDB-X also supports read-only columnar instances for querying columnar index data.