Here’s the last nail in the coffin. We hope this convinces you not to write to multiple masters with MySQL replication.
Reason 10 – No tools to reconcile inconsistent masters
For all the endless reasons we’ve already outlined MySQL replication is prone to failure. We know it’s going to happen, you now know too.
When replication breaks, your application may still be writing to both sides, both masters. Now you have data differences on both sides, random rows, in random tables.
Percona Toolkit checksum tool is great when you have a single authoritative master. It can compare & show you diffs. But when you’ve changed two masters, you have no authoritative side. Neither one is the last word on your data. You’re then faced with an intractable problem of reconciling your data in some manual or do-it-yourself method.
Not only would such a scenario be hairy and prone to error, but you would effectively have an outage for the duration. All ugly scenarios to be sure.
Click through to the end for multi-master solutions that work with MySQL.