Master&#x2F;master looks good on paper and glossy product hand-outs, but it doesn&#x27;t work out well in production. You&#x27;ll find every case or performance problem that causes it all to break horribly.<p>Facebook doesn&#x27;t do master-master on their MySQL instances. It&#x27;s all master-slave(s). Why? Because it works, it&#x27;s reliable, and it&#x27;s easy to change masters quickly when you have Facebook&#x27;s automation infrastructure.