MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0

18.8.3.2 Upgrading a Group Replication Member

This section explains the steps required for upgrading a member of a group. This procedure is part of the methods described at Section 18.8.3.3, “Group Replication Online Upgrade Methods”. The process of upgrading a member of a group is common to all methods and is explained first. The way which you join upgraded members can depend on which method you are following, and other factors such as whether the group is operating in single-primary or multi-primary mode. How you upgrade the server instance, using either the in-place or provision approach, does not impact on the methods described here.

The process of upgrading a member consists of removing it from the group, following your chosen method of upgrading the member, and then rejoining the upgraded member to a group. The recommended order of upgrading members in a single-primary group is to upgrade all secondaries, and then upgrade the primary last. If the primary is upgraded before a secondary, a new primary using the older MySQL version is chosen, but there is no need for this step.

To upgrade a member of a group:

When an upgraded member joins a group which has any member running an earlier MySQL Server version, the upgraded member joins with super_read_only=on. This ensures that no writes are made to upgraded members until all members are running the newer version. In a multi-primary mode group, when the upgrade has been completed successfully and the group is ready to process transactions, members that are intended as writeable primaries must be set to read-write mode. From MySQL 8.0.17, when all members of a group have been upgraded to the same release, they all change back to read-write mode automatically. For earlier releases you must set each member manually to read-write mode. Connect to each member and issue:

SET GLOBAL super_read_only=OFF;