MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0

18.9 Group Replication System Variables

This section lists the system variables that are specific to the Group Replication plugin. Every configuration option is prefixed with "group_replication".


InnoDB Cluster uses Group Replication, but the default values of the Group Replication system variables may differ from the defaults documented in this section. For example, in InnoDB Cluster, the default value of group_replication_communication_stack is MYSQL, not XCOM as it is for a default Group Replication implementation.

For more information, see MySQL InnoDB Cluster.

Some system variables on a Group Replication group member, including some Group Replication-specific system variables and some general system variables, are group-wide configuration settings. These system variables must have the same value on all group members, and require a full reboot of the group (a bootstrap by a server with group_replication_bootstrap_group=ON) in order for the value change to take effect. For instructions to reboot a group where every member has been stopped, see Section 18.5.2, “Restarting a Group”.

If a running group has a value set for a group-wide configuration setting, and a joining member has a different value set for that system variable, the joining member cannot join the group until the value is changed to match. If the group has a value set for one of these system variables, and the joining member does not support the system variable, it cannot join the group.

The following system variables are group-wide configuration settings:

Group-wide configuration settings cannot be changed by the usual methods while Group Replication is running. However, from MySQL 8.0.16, you can use the group_replication_switch_to_single_primary_mode() and group_replication_switch_to_multi_primary_mode() functions to change the values of group_replication_single_primary_mode and group_replication_enforce_update_everywhere_checks while the group is still running. For more information, see Section, “Changing a Group's Mode”.

Most system variables for Group Replication can have different values on different group members. For the following system variables, it is advisable to set the same value on all members of a group in order to avoid unnecessary rollback of transactions, failure of message delivery, or failure of message recovery:

Most system variables for Group Replication are described as dynamic, and their values can be changed while the server is running. However, in most cases, the change only takes effect after you stop and restart Group Replication on the group member using a STOP GROUP_REPLICATION statement followed by a START GROUP_REPLICATION statement. Changes to the following system variables take effect without stopping and restarting Group Replication:

When you change the values of any Group Replication system variables, bear in mind that if there is a point where Group Replication is stopped on every member at once by a STOP GROUP_REPLICATION statement or system shutdown, the group must be restarted by bootstrapping as if it was being started for the first time. For instructions to do this safely, see Section 18.5.2, “Restarting a Group”. In the case of group-wide configuration settings, this is required, but if you are changing other settings, try to ensure at least one member is running at all times.

  • A number of system variables for Group Replication are not completely validated during server startup if they are passed as command line arguments to the server. These system variables include group_replication_group_name, group_replication_single_primary_mode, group_replication_force_members, the SSL variables, and the flow control system variables. They are only fully validated after the server has started.

  • System variables for Group Replication that specify IP addresses or host names for group members are not validated until a START GROUP_REPLICATION statement is issued. Group Replication's Group Communication System (GCS) is not available to validate the values until that point.

The system variables that are specific to the Group Replication plugin are as follows:

Group Replication Status Variable

This section describes the status variable which provides information about Group Replication. The variable has the following meaning: