Enable the failover with hot replica feature on existing read-only nodes in the PolarDB console to reduce failover time from about 20–30 seconds to 3–10 seconds.
Prerequisites
Before you begin, make sure that:
Your cluster runs one of the following versions:
Engine Minimum revision version PolarDB for MySQL 5.6 5.6.1.0.35 or later PolarDB for MySQL 5.7 5.7.1.0.24 or later PolarDB for MySQL 8.0.1 8.0.1.1.29 or later PolarDB for MySQL 8.0.2 8.0.2.2.12 or later Your cluster uses PolarProxy version 2.8.3 or later.
Usage notes
The hot replica node specifications must match those of the primary node.
Applications must support automatic reconnection. Without hot replica, a failover interrupts services for about 20–30 seconds. With hot replica enabled, failover completes within 3–10 seconds.
The Voting Disk Service (VDS) module used by the failover with hot replica feature conflicts with the In-Memory Column Index (IMCI) feature in certain versions:
Revision version Hot replica + IMCI behavior 8.0.1.1.42 or later, or 8.0.2.2.23 or later Hot replica and IMCI can coexist — but only if hot replica is enabled first. If a read-only IMCI node already exists in the cluster, you cannot enable hot replica on any read-only node. Earlier than 8.0.1.1.42, or earlier than 8.0.2.2.23 Hot replica and IMCI cannot be used together. If hot replica is enabled, you cannot add read-only IMCI nodes. If a read-only IMCI node already exists, you cannot enable hot replica on any read-only node. To resolve the conflict, delete the read-only column store node first. To add a read-only IMCI node when VDS conflicts, contact support to disable VDS. All nodes restart automatically while VDS is being disabled.
Enable hot replica on a read-only node
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.
Log on to the PolarDB console. In the left-side navigation pane, click Clusters. Select the cluster's region in the upper-left corner, then click the cluster ID to go to its Basic Information page.
In the Database Nodes section of the Basic Information page, click the
icon in the upper-right corner of the section to switch views.Find the read-only node for which you want to enable hot replica, then click Enable Hot Replica in the Actions column.
