17.4.1 Deploying in Multi-Primary or Single-Primary Mode
Group Replication operates in the following different modes:
The default mode is single-primary. It is not possible to have members of the group deployed in different modes, for example one configured in multi-primary mode while another one is in single-primary mode. To switch between modes, the group and not the server, needs to be restarted with a different operating configuration. Regardless of the deployed mode, Group Replication does not handle client-side fail-over, that must be handled by the application itself, a connector or a middleware framework such as a proxy or MySQL Router 8.0 .
When deployed in multi-primary mode, statements are checked to ensure they are compatible with the mode. The following checks are made when Group Replication is deployed in multi-primary mode:
If a transaction is executed under the SERIALIZABLE isolation level, then its commit fails when synchronizing itself with the group.
If a transaction executes against a table that has foreign keys with cascading constraints, then the transaction fails to commit when synchronizing itself with the group.
These checks can be deactivated by setting the option
FALSE. When deploying in single-primary mode, this option must be set to