A replication group uses a Group Replication communication protocol version that can differ from the MySQL Server version of the members. To check the group's communication protocol version, issue the following statement on any member:
The return value shows the oldest MySQL Server version that can
join this group and use this group's communication
protocol. MySQL 8.2 allows compression and
fragmentation of messages. The
function returns the minimum MySQL version that the group
supports; this might differ from the version number that was
passed to the
function, from the MySQL Server version that is installed on the
member where you use the function, or both.
When you upgrade all the members of a replication group to a new
MySQL Server release, the Group Replication communication
protocol version is not automatically upgraded, in case there is
still a requirement to allow members at earlier releases to
join. If you do not need to support older members and want to
allow the upgraded members to use any added communication
capabilities, after the upgrade use the
function to upgrade the communication protocol, specifying the
new MySQL Server version to which you have upgraded the members.
For more information, see
Section 18.104.22.168, “Setting a Group's Communication Protocol Version”.