PolarDB:Configure hot replica nodes

Scope of application

The failover with hot replica feature is supported on the following PolarDB for MySQL versions:

• Engine version:

  • MySQL 5.6. The revision version must be 5.6.1.0.35 or later.

  • MySQL 5.7. The revision version must be 5.7.1.0.24 or later.

  • MySQL 8.0.1. The revision version must be 8.0.1.1.29 or later.

  • MySQL 8.0.2. The revision version must be 8.0.2.2.12 or later.

• PolarProxy version: 2.8.3 or later is required.

Usage notes

• If hot replica is not enabled on a read-only node, a transient interruption of about 20 to 30 seconds may occur during a primary/secondary failover. Make sure that your application supports automatic reconnection. If hot replica is enabled, the failover completes within 1 to 5 seconds.

• The hot replica node must have the same specifications as the primary node.

• The Voting Disk module of the high-availability feature used by failover with hot replica has certain mutual exclusion with the IMCI (In-Memory Column Index) feature in certain kernel versions. The details are as follows:

  • For clusters with a kernel version of 8.0.1.1.43 or later or 8.0.2.2.24 or later, the IMCI feature is fully compatible with the failover with hot replica feature.

  • For clusters with a kernel version of 8.0.1.1.42 or 8.0.2.2.23:

    • If the cluster already has a read-only node with the failover with hot replica feature enabled, you can add a read-only IMCI node to the cluster.

    • If the cluster already has a read-only IMCI node, you cannot enable the failover with hot replica feature for any read-only node in the cluster.

  • For clusters with a kernel version earlier than 8.0.1.1.42 or 8.0.2.2.23, the IMCI feature and the failover with hot replica feature are mutually exclusive:

    • If the cluster already has a read-only node with the failover with hot replica feature enabled, you cannot add a read-only IMCI node to the cluster.

      Note

      If you want to add a read-only IMCI node to the cluster, you can contact us to disable the Voting Disk high-availability module for the failover with hot replica feature. After the module is disabled, you can add the read-only IMCI node. Note that all nodes are automatically restarted during this process.

    • If the cluster already has a read-only IMCI node, you cannot enable the failover with hot replica feature for any read-only node in the cluster.

  Note

  If IMCI and hot replica are mutually exclusive and you want to enable failover with hot replica for the cluster, delete the existing IMCI read-only node first.

Procedure

1. Log in to the PolarDB console，In the navigation pane on the left, click Clusters. Select the Region where the cluster is deployed, and then click the cluster ID to go to the cluster details page。

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

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

   Note

   The first time you enable hot replica on any node in the cluster, all nodes restart one by one. Subsequent enable or disable operations do not trigger a restart.