server_id重复导致报错

[xiaocy91]

        cursor.execute("SELECT @@server_id")
        self.server_id = cursor.fetchone()[0]

this code will report an error:
slave with uuid/ id as this slave has connected to the master.

mean that slave id is repeated.
why sever_id must be the same in binlog2sql ?
should the server id be unique?