How do I keep 2 scratch Databases in sync

My question is a lot like this one. However I'm on MySQL and I'm looking for the "lowest tech" solution that I can find.

The situation is that I have 2 databases that should have the same data in them but they are updated primarily when they are not able to contact each other. I suspect that there is some sort of clustering or master/slave thing that would be able to sync them just fine. However in my cases that is major overkill as this is just a scratch DB for my own use.

What is a good way to do this?

My current approach is to have a Federated table on one of them and, every so often, stuff the data over the wire to the other with an insert/select. It get a bit convoluted trying to deal with primary keys and what not. (insert ignore seems to not work correctly)

p.s. I can easily build a query that selects the rows to transfer.

Solution

My current solution is

set up a federated table on the source box that grabs the table on the target box
set up a view on the source box that selects the rows to be updated (as a join of the federated table)
set up another federated table on the target box that grabs the view on the source box
issue an INSERT...SELECT...ON DUPLICATE UPDATE on the target box to run the pull.

I guess I could just grab the source table and do it all in one shot, but based on the query logs I've been seeing, I'm guessing that I'd end up with about 20K queries being run or about 100-300MB of data transfer depending on how things happen. The above setup sold result in about 4 queries and little more data transfered than actually needed to be.