Fatal error: Out of memory (allocated 6291456) (tried to allocate 7680 bytes)
This is usually caused by Wordpress, Drupal or other ridiculously inefficient CMS' out there, as a temporary fix you can increase PHP's memory limit but it's best to find the actual culprit, by disabling add-ons and other scripts etc...........
Many people aren't aware but recently Dual-Master Replication setups have become increasingly popular. That's because you get similar features and benefits of having a full-blown cluster (difficult to setup and maintain and requires I believe 3 servers just as controllers).
With a dual-master you just have a different off-set for the keys and you should be good, but of course there is the chance that at some point replication will halt because of an unexpected or unforseen error........