Automated dump and import
We can run a query in each table to dump data that is newer than the last date we checked
select * from table where version > lastUpdate
This would get all the records that have been updated since t he last update.
We could then import this data.
I don't know what to do about data that already exists, we would have to generate update record sql commands.
Whenever data is changed, update the lastUpdate field so that the next dump will cover that row.
The complexity of Multi-Master replication does not stop at looking up what's been new in other replica sites. We could make the data that was created on one node only editable via interacting with that node, but all created by every node replicated to all other nodes.