Yep, we did MySQL dual primary-primary circular replication on a cluster with ten read replicas, thousands of qps per box, all the way back in 2005. We failed

Yep, we did MySQL dual primary-primary circular replication on a cluster with ten read replicas, thousands of qps per box, all the way back in 2005. We failed over back and forth from one primary to the other on a schedule every few weeks, just to practice and affirm we could.