PolarDB:Configure hot replica nodes

Supported versions

Your PolarDB for MySQL cluster runs the following versions:

• Database engine version:

  • PolarDB for MySQL 5.6 with a revision version of 5.6.1.0.35 or later.

  • PolarDB for MySQL 5.7 with a revision version of 5.7.1.0.24 or later.

  • PolarDB for MySQL 8.0.1 with a revision version of 8.0.1.1.29 or later.

  • PolarDB for MySQL 8.0.2 with a revision version of 8.0.2.2.12 or later.

• PolarProxy version: 2.8.3 or later.

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 during a failover. Therefore, make sure that your applications can be automatically reconnected to the cluster. If the hot replica feature is enabled for read-only nodes, a 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 Voting Disk Service (VDS) module of the failover with hot replica feature is mutually exclusive with the In-Memory Column Index (IMCI) feature in specific database engine versions.

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

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

    • If a read-only IMCI 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 IMCI nodes to the cluster.

      Note

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

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

Procedure

1. Log on to the PolarDB console. Click Clusters in the left-side navigation pane. Select the region of the cluster in the upper-left corner and click the ID of the cluster in the list to go to its Basic Information page.

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

3. 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.

   

   Note

   The first time when the failover with hot replica feature is enabled, 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.