When chatting with Denis Creighton and the technical team in FEXCO (who also use MySQL inhouse as well as bxp) we discovered that MySQL 5.7 had some distinct advantages over 5.6.
The master / slave functionality now means that in real time Db2 can serve as a database server. It is also now capable of responding to queries, thus allowing it to become operational rather than just a backup server waiting in the wings.
== Operational challenges ==