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2.2.5.1 Setting the Replica Configuration

Each replica must have a unique server ID, as specified by the server_id system variable. If you are setting up multiple replicas, each one must have a unique server_id value that differs from that of the source and from any of the other replicas. If the replica's server ID is not already set, or the current value conflicts with the value that you have chosen for the source server or another replica, you must change it. With the default server_id value of 0, a replica refuses to connect to a source.

You can change the server_id value dynamically by issuing a statement like this:

SET GLOBAL server_id = 21;

If the default server_id value of 0 was set previously, you must restart the server to initialize the replica with your new nonzero server ID. Otherwise, a server restart is not needed when you change the server ID, unless you make other configuration changes that require it. For example, if binary logging was disabled on the server and you want it enabled for your replica, a server restart is required to enable this.

If you are shutting down the replica server, you can edit the [mysqld] section of the configuration file to specify a unique server ID. For example:

[mysqld]
server-id=21

A replica is not required to have binary logging enabled for replication to take place. However, binary logging on a replica means that the replica's binary log can be used for data backups and crash recovery. Replicas that have binary logging enabled can also be used as part of a more complex replication topology. If you want to enable binary logging on a replica, use the log-bin option in the [mysqld] section of the configuration file. A server restart is required to start binary logging on a server that did not previously use it.