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PolarDB:Configure hot replica nodes

Last Updated:Jun 18, 2024

You cannot directly set hot replica nodes when you create a cluster. You can only enable the failover with hot replica feature for existing read-only nodes in your cluster.

Prerequisites

  • Your cluster is a PolarDB for MySQL Enterprise Edition cluster. It meets one of the following cluster version requirements:

    • The PolarDB cluster runs MySQL 5.6 and the revision version is 5.6.1.0.35 or later.

    • The PolarDB cluster runs MySQL 5.7 and the revision version is 5.7.1.0.24 or later.

    • The PolarDB cluster runs MySQL 8.0.1 and the revision version is 8.0.1.1.29 or later.

    • The PolarDB cluster runs MySQL 8.0.2 and the revision version is 8.0.2.2.12 or later.

  • PolarDB for MySQL PolarProxy is 2.8.1 or later. For more information about how to view and update the PolarProxy version, see Upgrade the cluster version.

Precautions

  • If the failover with hot replica feature is not enabled for read-only nodes, your services may be interrupted for about 20 to 30 seconds when failover occurs. Therefore, make sure that your applications can be automatically reconnected to the cluster. If the hot replica feature is enabled for read-only nodes, failover can be completed within 3 to 10 seconds.

  • The specifications of hot replica nodes must be the same as those of the primary node.

  • The In-Memory Column Index (IMCI) feature cannot be used together with the Voting Disk Service (VDS) module of the failover with hot replica feature.

    • For a cluster whose revision version is 8.0.1.1.42 and later or 8.0.2.2.23 and later:

      • If a cluster contains a read-only node where the failover with hot replica feature is enabled, you can add read-only column store nodes to the cluster.

      • If a read-only column store node already exists in a cluster, you cannot enable the hot standby feature for any read-only node in the cluster.

    • For a cluster whose revision version is earlier than 8.0.1.1.42 or earlier than 8.0.2.2.23, the IMCI feature cannot be used together with failover with hot replica feature.

      • If a cluster contains a read-only node for which the failover with hot replica feature is enabled, you cannot add read-only column store nodes to the cluster.

        Note

        If you want to add a read-only column store node to the cluster, contact the technical support to disable VDS. When VDS is being disabled, all nodes in the cluster are automatically restarted.

      • If a read-only column store node already exists in a cluster, you cannot enable the hot standby feature for any read-only node in the cluster.

    Note

    If you want to enable the failover with hot replica feature for the cluster, delete the read-only column store node first.

  • To enable the transaction status preservation feature, you must set the loose_innodb_trx_resume parameter to ON on the Parameters page in the PolarDB console. For more information, see Specify cluster and node parameters.

Procedure

  1. Log on to the PolarDB console.

  2. In the upper-left corner, select the region where the cluster is deployed.

  3. Find the cluster and click its ID.

  4. In the Database Nodes section of the Basic Information page, click the 切换 icon in the upper-right corner of the section to switch views.

  5. In the Database Nodes section, find the read-only node for which you want to enable hot replica and click Enable Hot Replica in the Actions column.

    开启热备

    Note

    When the failover with hot replica feature is enabled for the first time, all nodes in the cluster are restarted one by one. Subsequentially, anytime the failover with hot replica feature is enabled or disabled, the nodes are not restarted.