Configuring an Online Group SELECT group_replication_set_write_concurrency( instances ); SELECT group_replication_get_communication_protocol(); +------------------------------------------------+ | group_replication_get_communication_protocol() | +------------------------------------------------+ | 8.0.16 | +------------------------------------------------+ 3728 Note that the  group_replication_get_communication_protocol()  function returns the minimum MySQL version that the group supports, which might differ from the version number that was passed to the  group_replication_set_communication_protocol()  function, and from the MySQL Server version that is installed on the member where you use the function. You can inspect the communication protocol in use by a group by using the group_replication_get_communication_protocol()  function, which returns the oldest MySQL Server version that the group supports. All existing members of the group return the same communication protocol version. For example: If two members attempt to join in the same membership change event, they can only join if the communication protocol version for both members is already compatible with the group’s communication protocol version. Members with different communication protocol versions from the group must join in isolation. For example: A MySQL server at version X can only join and reach  ONLINE  status in a replication group if the group’s communication protocol version is less than or equal to X. When a new member joins a replication group, it checks the communication protocol version that is announced by the existing members of the group. If the joining member supports that version, it joins the group and uses the communication protocol that the group has announced, even if the member supports additional communication capabilities. If the joining member does not support the communication protocol version, it is expelled from the group. From MySQL 8.0.16, Group Replication has the concept of a communication protocol for the group. The Group Replication communication protocol version can be managed explicitly, and set to accommodate the oldest MySQL Server version that you want the group to support. This enables groups to be formed from members at different MySQL Server versions while ensuring backward compatibility. Versions from MySQL 5.7.14 allow compression of messages, and versions from MySQL 8.0.16 also allow fragmentation of messages. All members of the group must use the same communication protocol version, so that group members can be at different MySQL Server releases but only send messages that can be understood by all group members. where  instances  is the new maximum number of consensus instances. The GROUP_REPLICATION_ADMIN  privilege is required to use this function. 18.5.1.4 Setting a Group’s Communication Protocol Version •One MySQL Server 8.0.16 instance can successfully join a group that uses the communication protocol version 5.7.24. •One MySQL Server 5.7.24 instance cannot successfully join a group that uses the communication protocol version 8.0.16. •Two MySQL Server 8.0.16 instances cannot simultaneously join a group that uses the communication protocol version 5.7.24. •Two MySQL Server 8.0.16 instances can simultaneously join a group that uses the communication protocol version 8.0.16.