Open Source Multi-master replication ideas? I have multiple geographically separated data centres on a private network and would like some ideas for WAN outage tolerant open-source multi-master replication databases. I'm OK with RAM only dbs.

I need to be able to write to a common table on the local master at each data centre and have that information change in all versions of that table in all the data centres.

During a WAN outage I need to be able to continue to write to this common table at each data centre locally. When WAN connectivity resumes I need it to automatically merge all the changes together with some kind of conflict resolution.

Handling latency degregation would be an optional plus.

Is MySQL Cluster Multi-Site Clustering what I'm looking for? I find it hard to figure it out from their documentation.

I don't need an SQL interface or MySQL specifically, simple key:value would work too.

I really hope some more knowledgeable people could point me in the right direction!
I favor Galera clustering (see Percona's PXC or MariaDB).  Put 1 node in each of 3 different datacenters.  (One node could be a trivial 'arbitrator' if you need to cut corners.)

Galera requires the use of InnoDB, but that is reasonably efficient.

If a node goes down, or is separated from the other two nodes due to a network outage, the system hums along, with the restriction that you can't write to the dead/isolated node.  When if comes back up (or is replaced/repaired), the cluster will repair it automagically.

If no node can talk to any other node (which seems extreme), manual intervention will be required.  (Actually, if more that 50% of the nodes are communicating with each other, the "system" is still alive and usable.)

Transactions are synchronous (read: latency), but there in only one round trip per transaction.

NDB Cluster (which is perhaps what you are referring to) is a distinctly different animal.  It uses an "eventual consistency" for dealing with replication.  This is not at all related to the rest of MySQL replication options.

Key:value can be implemented easily on top of InnoDB or NDB cluster.