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 the group's communication protocol.
Versions from MySQL 5.7.14 allow compression of messages, and
versions from MySQL 8.0.16 also allow fragmentation of messages.
Note that the
UDF returns the minimum MySQL version that the group supports,
which might differ from the version number that was passed to
UDF, and from the MySQL Server version that is installed on the
member where you use the UDF.
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
UDF to upgrade the communication protocol, specifying the new
MySQL Server version to which you have upgraded the members. For
more information, see
Section 220.127.116.11, “Setting a Group's Communication Protocol Version”.